@article{KleinpeterKoch2013, author = {Kleinpeter, Erich and Koch, Andreas}, title = {(Anti)aromaticity of dehydroannulenes of various ring size proved by the ring current effect in H-1 NMR spectra}, series = {Tetrahedron}, volume = {69}, journal = {Tetrahedron}, number = {5}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2012.12.019}, pages = {1481 -- 1488}, year = {2013}, abstract = {The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of already synthesized dehydro[n]annulenes of various ring size (from C-12 to C-20) have been computed, visualized as Isochemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to present (anti)aromaticity. For this purpose the thus quantified ring current effect of the macro cycles on proximate protons in proton NMR spectra was employed.}, language = {en} } @article{KammerStarkePietruchaetal.2012, author = {Kammer, Stefan and Starke, Ines and Pietrucha, Andreas and Kelling, Alexandra and Mickler, Wulfhard and Schilde, Uwe and Dosche, Carsten and Kleinpeter, Erich and Holdt, Hans-J{\"u}rgen}, title = {1,12-Diazaperylene and 2,11-dialkylated-1,12-diazaperylene iridium(III) complexes [Ir((CN)-N-boolean AND)(2)((NN)-N-boolean AND)]PF6: new supramolecular assemblies}, series = {Dalton transactions : a journal of inorganic chemistry, including bioinorganic, organometallic, and solid-state chemistry}, volume = {41}, journal = {Dalton transactions : a journal of inorganic chemistry, including bioinorganic, organometallic, and solid-state chemistry}, number = {34}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1477-9226}, doi = {10.1039/c2dt30412k}, pages = {10219 -- 10227}, year = {2012}, abstract = {A series of new monocationic iridium(III) complexes [Ir((CN)-N-boolean AND)(2)((NN)-N-boolean AND)]PF6 with "large-surface" alpha,alpha'-diimin ligands (NN)-N-boolean AND (dap = 1,12-diazaperylene, dmedap = 2,11-dimethyl-1,12-diazaperylene, dipdap = 2,11-diisopropyl-1,12-diazaperylene) and different cyclometalating ligands (CN)-N-boolean AND (piq = 1-phenylisoquinoline, bzq = benzo[h]quinoline, ppz = 1-phenylpyrazole, thpy = 2-(2-thienyl)pyridine, ppy = 2-phenylpyridine, meppy = 2-(4-methylphenyl)pyridine, dfppy = 2-(2,4-difluorophenyl)pyridine) were synthesized. The solid structures of the complexes [Ir(piq)(2)(dap)]PF6, [Ir(bzq)(2)(dap)]PF6, [Ir(ppy)(2)(dipdap)]PF6, [Ir(piq)(2)(dmedap)]PF6, [Ir(ppy)(2)(dap)]PF6 and [Ir(ppz)(2)(dap)]PF6 are reported. In [Ir(piq)(2)(dap)]PF6, the dap ligand and one of the piq ligands of each cationic complex are involved in pi-pi stacking interactions forming supramolecular channels running along the crystallographic c axis. In the crystalline [Ir(bzq)(2)(dap)]PF6 pi-pi stacking interactions between the metal complexes lead to the formation of a 2D layer structure. In addition, CH-pi interactions were found in all compounds, which are what stabilizes the solid structure. In particular, a significant number of them were found in [Ir(piq)(2)(dap)]PF6 and [Ir(bzq)(2)(dap)]PF6. The crystal structures of [Ir(ppy)(2)(dipdap)]PF6 and [Ir(ppy)(2)(dmedap)]PF6 are also presented, being the first examples of bis-cyclometalated iridium(III) complexes with phenanthroline-type alpha,alpha'-diimin ligands bearing bulky alkyl groups in the neighbourhood of the N-donor atoms. These ligands implicate a distorted octahedral coordination geometry that in turn destabilized the Ir-N-N boolean AND N bonds. The new iridium (III) complexes are not luminescent. All compounds show an electrochemically irreversible anodic peak between 1.15 and 1.58 V, which is influenced by the different cyclometalated ligands. All of the new complexes show two reversible successive one-electron "large-surface" ligand-centred reductions around -0.70 V and -1.30 V. Electrospray ionisation mass spectrometry (ESI-MS) and collision induced decomposition (CID) measurements were used to investigate the stability of the new complexes. Thereby, the stability agreed well with the order of the Ir-N-N boolean AND N bond lengths.}, language = {en} } @article{ShainyanKirpichenkoKleinpeteretal.2013, author = {Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Kleinpeter, Erich and Shlykov, Sergey A. and Osadchiy, Dmitriy Yu and Chipanina, Nina N. and Oznobikhina, Larisa P.}, title = {1,3-Dimethy1-3-silapiperidine - synthesis, molecular structure, and conformational analysis by gas-phase electron diffraction, low temperature NMR, IR and Raman Spectroscopy, and quantum chemical calculations}, series = {The journal of organic chemistry}, volume = {78}, journal = {The journal of organic chemistry}, number = {8}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/jo400289g}, pages = {3939 -- 3947}, year = {2013}, abstract = {The first Si-H-containing azasilaheterocycle, 1,3-dimethyl-3-silapiperidine 1, was synthesized, and its molecular structure and conformational properties were studied by gas-phase electron diffraction (GED), low temperature NMR, IR and Raman spectroscopy and quantum chemical calculations. The compound exists as a mixture of two conformers possessing the chair conformation with the equatorial NMe group and differing by axial or equatorial position of the SiMe group. In the gas phase, the SiMeax conformer predominates (GED: ax/eq = 65(7):35(7)\%,Delta G = 0.36(18) kcal/mol; IR: ax/eq = 62(5):38(5)\%,Delta G = 0.16(7) kcal/mol). In solution, at 143 k the SiMeeq conformer predominates' in the frozen equilibrium (NMR: ax/eq = 31.5(1.5):68.5(1.5)\%, Delta G = -0.22(2) kcal/mol). Thermodynamic parameters of the ring inversion are determined (Delta G(double dagger) = 8.9-9.0 kcal/mol, Delta H-double dagger = 9.6 kcal/mol, Delta S-double dagger = 2.1 eu). High-level quantum chemical calculations :(MP2, G2, CCSD(T)) nicely reproduce the experimental geometry and the predominance of the axial conformer in the gas phase.}, language = {en} } @article{ShainyanSuslovaTranDinhPhienetal.2019, author = {Shainyan, Bagrat A. and Suslova, Elena N. and Tran Dinh Phien, and Shlykov, Sergey A. and Heydenreich, Matthias and Kleinpeter, Erich}, title = {1-Methylthio-1-phenyl-1-silacyclohexane: Synthesis, conformational preferences in gas and solution by GED, NMR and theoretical calculations}, series = {Tetrahedron}, volume = {75}, journal = {Tetrahedron}, number = {46}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2019.130677}, pages = {9}, year = {2019}, abstract = {1-Methylthio-1-phenyl-1-silacyclohexane 1, the first silacyclohexane with the sulfur atom at silicon, was synthesized and its molecular structure and conformational preferences studied by gas-phase electron diffraction (GED) and low temperature C-13 and Si-29 NMR spectroscopy (LT NMR). Quantum-chemical calculations were carried out both for the isolated species and solvate complexes in gas and in polar medium. The predominance of the 1-MeSaxPheq conformer in gas phase (1-Ph-eq :1-Ph-ax = 55:45, Delta G degrees = 0.13 kcal/mol) determined from GED is consistent with that measured in the freon solution by LT NMR (1-Ph-eq:1-Ph-ax = 65:35, Delta G degrees = 0.12 kcal/mol), the experimentally measured ratios being close to that estimated by quantum chemical calculations at both the DFT and MP2 levels of theory. (C) 2019 Elsevier Ltd. All rights reserved.}, language = {en} } @article{PihlajaSinkkonenStajeretal.2011, author = {Pihlaja, Kalevi and Sinkkonen, Jari and Stajer, Geza and Koch, Andreas and Kleinpeter, Erich}, title = {1-Oxo-1,3-dithiolanes - synthesis and stereochemistry}, series = {Magnetic resonance in chemistry}, volume = {49}, journal = {Magnetic resonance in chemistry}, number = {7}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0749-1581}, doi = {10.1002/mrc.2764}, pages = {443 -- 449}, year = {2011}, abstract = {1-Oxo-1,3-dithiolane (4) and its cis- and trans-2-methyl (5,6), -4-methyl (7,8) and -5-methyl (9,10) derivatives were prepared by oxidizing the corresponding 1,3-dithiolanes (1-3) with NaIO(4) in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with (1)H and (13)C NMR spectroscopy and molecular modelling. The sulfoxides 4-6 and 8-10 attain two S(1) type envelopes (sometimes slightly distorted) the S=O(ax) envelope greatly dominating. Cis-4-methyl-1-oxo-1,3-dithiolane is a special case exhibiting both two closely related S=O(ax) (30 and 27\%) as well as S=O(eq) (21 and 22\%) forms [S(1) and C(4) envelopes, respectively]. The relative energies of these conformations, the values of (1)H-(1)H coupling constants and (1)H and (13)C chemical shifts were estimated by computational methods and they support well the conclusions based on the experimental data.}, language = {en} } @article{KleinpeterPihlajaSinkkonenetal.2011, author = {Kleinpeter, Erich and Pihlaja, Kalevi and Sinkkonen, Jari and St{\´a}jer, Gez{\´a} and Koch, Andreas}, title = {1-Oxo-1,3-dithiolanes{\`u}synthesis and stereochemistry}, issn = {0749-1581}, year = {2011}, abstract = {1-Oxo-1,3-dithiolane (4) and its cis- andtrans-2-methyl (5,6), -4-methyl (7,8) and -5-methyl (9,10) derivatives were prepared by oxidizing the corresponding 1,3-dithiolanes (1-3) with NaIO4 in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with 1H and 13C NMR spectroscopy and molecular modelling. The sulfoxides 4-6 and 8-10 attain two S(1) type envelopes (sometimes slightly distorted) the S=Oax envelope greatly dominating. Cis-4-methyl-1-oxo-1,3-dithiolane is a special case exhibiting both two closely related S=Oax (30 and 27\%) as well as S=Oeq (21 and 22\%) forms [S(1) and C(4) envelopes, respectively]. The relative energies of these conformations, the values of 1H-1H coupling constants and 1H and 13C chemical shifts were estimated by computational methods and they support well the conclusions based on the experimental data.}, language = {en} } @article{ThomasBruehlHeilmannetal.1997, author = {Thomas, Steffen and Br{\"u}hl, Iris and Heilmann, Dieter and Kleinpeter, Erich}, title = {13 C NMR Chemical shift calculations for some substituted pyridines - a comparative consideration}, year = {1997}, language = {en} } @article{KleinpeterKochFischeretal.1997, author = {Kleinpeter, Erich and Koch, Andreas and Fischer, G. and Askolin, C.-P.}, title = {13 C NMR, 15 N NMR and quantum-chemical study of the tautomerism of 2-substituted 5-ME-7-OH-1,2,4-triazolo[1,5- a]pyrimidines}, year = {1997}, language = {en} } @article{KleinpeterThomasFischer1995, author = {Kleinpeter, Erich and Thomas, Steffen and Fischer, G.}, title = {13C and 15N NMR study of 1,2,4-Triazolo[1,5-a]pyrimidines with one tautomerism-introducing substituent}, year = {1995}, language = {en} } @book{PihlajaKleinpeter1994, author = {Pihlaja, Kalevi and Kleinpeter, Erich}, title = {13C NMR chemical shifts in structural and stereochemical analysis}, series = {Methods in stereochemical analysis}, journal = {Methods in stereochemical analysis}, publisher = {VCH}, address = {New York}, year = {1994}, language = {en} } @article{StroehlThomasRadegliaetal.1992, author = {Str{\"o}hl, D. and Thomas, Steffen and Radeglia, R. and Brunn, J. and Kleinpeter, Erich}, title = {13C-NMR-Untersuchungen von Substituenteneffekten in mehrfach substituierten Benz-und Naphthalenderivaten ; Inkrementberechnungen der 13C-chemischen Verschiebungen}, year = {1992}, language = {de} } @article{LehmannKleinpeter1995, author = {Lehmann, J. and Kleinpeter, Erich}, title = {1H NMR lanthanide-induced shift investigations of highly flexible molecules, part III. Applications to alcohols, aldehydes, esters and amines}, year = {1995}, language = {en} } @article{LehmannKleinpeter1993, author = {Lehmann, J. and Kleinpeter, Erich}, title = {1H NMR Lanthanideinduced Shift (LIS) investigations of highly flexible molecules : a new approach}, year = {1993}, language = {en} } @article{LehmannKleinpeter1993, author = {Lehmann, J. and Kleinpeter, Erich}, title = {1H NMR Lanthanideinduced Shift (LIS) investigations of highly flexible molecules : a new approach ; Part II}, year = {1993}, language = {en} } @article{HilfertSarodnickKempteretal.1998, author = {Hilfert, Liane and Sarodnick, Gerhard and Kempter, Gerhard and Kleinpeter, Erich}, title = {1H, 13C and 15 N NMR study and molecular modelling of 2,3- disubstituted quinoxalines with sterically hinderered aromatic and heteroaromatic substituents}, year = {1998}, language = {en} } @article{StarkeKochHoldtetal.1995, author = {Starke, Ines and Koch, Andreas and Holdt, Hans-J{\"u}rgen and Kleinpeter, Erich}, title = {1H, 13C, and 15N NMR study of the solution structure of metabridged bis(benzo-15-crown-5-ether)s}, year = {1995}, language = {en} } @article{DzambaskiMarkovicKleinpeteretal.2013, author = {Dzambaski, Zdravko and Markovic, Rade and Kleinpeter, Erich and Baranac-Stojanovic, Marija}, title = {2-Alkylidene-4-oxothiazolidine S-oxides - synthesis and stereochemistry}, series = {Tetrahedron}, volume = {69}, journal = {Tetrahedron}, number = {31}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2013.05.087}, pages = {6436 -- 6447}, year = {2013}, abstract = {A series of 5-unsubstituted and 5-substituted 2-alkylidene-4-oxothiazolidine-S-oxides were synthesized by the sulfur-oxidation with m-CPBA. The stereochemistry of 5-substituted sulfoxides was determined by means of NMR spectroscopy and DFT theoretical calculations. It was found that the thermodynamically less stable anti-isomer was initially formed in the course of the oxidation, but it underwent epimerization to the mixture enriched in the more stable syn-isomer, during the work-up process. The higher stability of syn-isomers is ascribed to the stronger hyperconjugative sigma(C-H)->sigma*(S-O) interaction versus the weaker sigma(C-C)->sigma*(S-O) delocalization in their anti-counterparts and to the existence of intramolecular 1,5-CH center dot center dot center dot C hydrogen bonds.}, language = {en} } @article{KolocourisKochKleinpeteretal.2015, author = {Kolocouris, Antonios and Koch, Andreas and Kleinpeter, Erich and Stylianakis, Ioannis}, title = {2-Substituted and 2,2-disubstituted adamantane derivatives as models for studying substituent chemical shifts and C-H-ax center dot center dot center dot Y-ax cyclohexane contacts-results from experimental and theoretical NMR spectroscopic chemical shifts and DFT structures}, series = {Tetrahedron}, volume = {71}, journal = {Tetrahedron}, number = {16}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.01.044}, pages = {2463 -- 2481}, year = {2015}, abstract = {The complete H-1 and C-13 NMR chemical shifts assignment for various 2-substituted and 2,2-disubstituted adamantane derivatives 1-38 in CDCl3 solution was realized on the basis of NMR experiments combined with chemical structure information and DFT-GIAO (B3LYP/6-31+G(d,p)-GIAO) calculations of chemical shifts in solution. Substituent-induced C-13 NMR chemical shifts (SCS) are discussed. C-H-ax center dot center dot center dot Y-ax contacts are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts will be further investigated in this work on basis of new adamantane derivatives, which are substituted at C-2 to provide models for 1,4-C-H-ax center dot center dot center dot Y-ax and 1,5-C-H-ax center dot center dot center dot Y-ax contacts. The B3LYP/6-31+G(d,p) calculations predicted the presence of NBO hyperconjugative attractive interactions between C-H-ax and Y-ax groups along C-H-ax center dot center dot center dot Y-ax contacts. The H-1 NMR signal separation, Delta delta(gamma-CH2), reflects the strength of the H-bonded C-H-ax center dot center dot center dot Y-ax contact. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{LazarevaShainyanKleinpeter2010, author = {Lazareva, Nataliya F. and Shainyan, Bagrat A. and Kleinpeter, Erich}, title = {4-Alkyl-2,2,6,6-tetramethyl-1,4,2,6-oxaazadisilinanes : synthesis, structure, and conformational analysis}, issn = {0894-3230}, doi = {10.1002/Poc.1605}, year = {2010}, abstract = {4-Alkyl-2,2,6,6-tetramethyl-1,4,2,6-oxaazadisilinanes RN[CH2Si(Me)2]2O [R = Me (1), i-Pr (2)] were synthesized by two methods which provided good yields up to 84\%. Low temperature NMR study of compounds (1) and (2) revealed a frozen ring inversion with the energy barriers of 8.5 and 7.7 kcal/mol at 163 and 143 K, respectively, which is substantially lower than that for their carbon analog, N-methylmorpholine. DFT calculations performed on the example of molecule (1) showed that N-Meax conformer to exist in the sofa conformation with the coplanar fragment C-Si-O-Si-C, and its N-Meeq conformer in a flattened chair conformation.}, language = {en} } @article{BalciKochKleinpeter2006, author = {Balci, Kubilay and Koch, Andreas and Kleinpeter, Erich}, title = {A comparative vibrational spectroscopic investigation of free mn-12S(2)O(2) and fn-12S(2)O(2) dithiacrown ethers based on DFT calculations}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2005.10.048}, year = {2006}, abstract = {A successful assignment for the fundamental bands observed in the experimental IR spectra of mn-12S(2)O(2) and fn-12S(2)O(2) dithiacrown ethers was achieved by the aid of the density functional theory (DFT) based quantum mechanical calculations carried out at the 133LYP/6-31G(d) and B3LYP/6-31 + G(d) level of theory. Two different scaling approaches, '(i) scaled quantum mechanics force field (SQM FF) methodology', and (ii) the 'scaling frequencies with dual empirical scale factors', were used in order to fit the calculated harmonic frequencies to the experimental ones. Potential energy distribution (PED) calculations were carried out to define the internal coordinate contributions to each normal mode and to define the corresponding normal modes of the molecules. The effects of the conformational differences onto the IR active normal modes of the two isomeric molecules and their corresponding experimental frequencies were discussed in the light of the calculated spectral data.}, language = {en} } @article{KleinpeterBalciYaparetal.2012, author = {Kleinpeter, Erich and Balci, Kubilay and Yapar, G. and Akkaya, S. and Akyuz, S. and Koch, Andreas}, title = {A conformational analysis and vibrational spectroscopic investigation on 1,2-bis(o-carboxyphenoxy) ethane molecule}, year = {2012}, abstract = {The minima on the potential energy surface of 1,2-bis(o-carboxyphenoxy) ethane (CPE) molecule in its electronic ground state were searched by a molecular dynamics simulation performed with MM2 force field. For each of the found minimum-energy conformers, the corresponding equilibrium geometry, charge distribution, HOMO-LUMO energy gap, force field, vibrational normal modes and associated IR and Raman spectral data were determined by means of the density functional theory (DFT) based electronic structure calculations carried out by using B3LYP method and various Pople- style basis sets. The obtained theoretical data confirmed the significant effects of the intra- and inter-molecular hydrogen bonding interactions on the conformational structure, force field, and group vibrations of the molecule. The same data have also revealed that two of the determined stable conformers, both of which exhibit pseudo-crown structure, are considerably more favorable in energy to the others and accordingly provide the major c ntribution to the experimental spectra of CPE. In the light of the improved vibrational spectral data obtained within the "SQM FF" methodology and "Dual Scale Factors" approach for the monomer and dimer forms of these two conformers, a reliable assignment of the fundamental bands observed in the experimental room-temperature IR and Raman spectra of the molecule was given, and the sensitivities of its group vibratb20s to conformation, substitution and dimerization were discussed.}, language = {en} } @article{BalciYaparAkkayaetal.2012, author = {Balci, Kubilay and Yapar, G. and Akkaya, Y. and Akyuz, S. and Koch, Andreas and Kleinpeter, Erich}, title = {A conformational analysis and vibrational spectroscopic investigation on 1,2-bis(o-carboxyphenoxy) ethane molecule}, series = {Vibrational spectroscopy : an international journal devoted to applications of infrared and raman spectroscopy}, volume = {58}, journal = {Vibrational spectroscopy : an international journal devoted to applications of infrared and raman spectroscopy}, number = {1-2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0924-2031}, doi = {10.1016/j.vibspec.2011.11.011}, pages = {27 -- 43}, year = {2012}, abstract = {The minima on the potential energy surface of 1,2-bis(o-carboxyphenoxy)ethane (CPE) molecule in its electronic ground state were searched by a molecular dynamics simulation performed with MM2 force field. For each of the found minimum-energy conformers, the corresponding equilibrium geometry, charge distribution, HOMO-LUMO energy gap, force field, vibrational normal modes and associated IR and Raman spectral data were determined by means of the density functional theory (DFT) based electronic structure calculations carried out by using B3LYP method and various Pople-style basis sets. The obtained theoretical data confirmed the significant effects of the intra- and inter-molecular hydrogen bonding interactions on the conformational structure, force field, and group vibrations of the molecule. The same data have also revealed that two of the determined stable conformers, both of which exhibit pseudo-crown structure, are considerably more favorable in energy to the others and accordingly provide the major contribution to the experimental spectra of CPE. In the light of the improved vibrational spectral data obtained within the "SQM FF" methodology and "Dual Scale Factors" approach for the monomer and dimer forms of these two conformers, a reliable assignment of the fundamental bands observed in the experimental room-temperature IR and Raman spectra of the molecule was given, and the sensitivities of its group vibrations to conformation, substitution and dimerization were discussed.}, language = {en} } @article{KramerKleinpeter2013, author = {Kramer, Markus and Kleinpeter, Erich}, title = {A conformational study of N-acetyl glucosamine derivatives utilizing residual dipolar couplings}, issn = {1090-7807}, year = {2013}, language = {en} } @article{KramerKleinpeter2011, author = {Kramer, Markus and Kleinpeter, Erich}, title = {A conformational study of N-acetyl glucosamine derivatives utilizing residual dipolar couplings}, series = {Journal of magnetic resonance}, volume = {212}, journal = {Journal of magnetic resonance}, number = {1}, publisher = {Elsevier}, address = {San Diego}, issn = {1090-7807}, doi = {10.1016/j.jmr.2011.06.029}, pages = {174 -- 185}, year = {2011}, abstract = {The conformational analyses of six non-rigid N-acetyl glucosamine (NAG) derivatives employing residual dipolar couplings (RDCs) and NOEs together with molecular dynamics (MD) simulations are presented. Due to internal dynamics we had to consider different conformer ratios existing in solution. The good quality of the correlation between theoretically and experimentally obtained RDCs show the correctness of the calculated conformers even if the ratios derived from the MD simulations do not exactly meet the experimental data. If possible, the results were compared to former published data and commented.}, language = {en} } @misc{KramerKleinpeter2011, author = {Kramer, Markus and Kleinpeter, Erich}, title = {A conformational study of N-acetyl glucosamine derivatives utilizing residual dipolar couplings (vol 212, pg 174, 2011)}, series = {Journal of magnetic resonance}, volume = {213}, journal = {Journal of magnetic resonance}, number = {1}, publisher = {Elsevier}, address = {San Diego}, issn = {1090-7807}, doi = {10.1016/j.jmr.2011.09.017}, pages = {210 -- 211}, year = {2011}, language = {en} } @article{ThomasKleinpeter2005, author = {Thomas, Steffen and Kleinpeter, Erich}, title = {A novel empirical approach for the structure elucidation of disilanes by empirical estimation of their Si-29 chemical shifts}, issn = {0022-2860}, year = {2005}, abstract = {In C-13 NMR spectroscopy, there are many empirical methods for fast and exact computation of C-13 chemical shifts; comparable procedures for Si-29 NMR chemical shifts are not existing or are older than 20 years. On basis of the largest database of Si-29 chemical shifts available, along this paper a relatively simple procedure for the similarly exact calculation of the Si-29 chemical shifts of disilanes (average margin of error ca. 3.7 ppm) is given. (c) 2005 Elsevier B.V. All rights reserved}, language = {en} } @article{DrexlerGrotjahnKleinpeteretal.1999, author = {Drexler, Hans-Joachim and Grotjahn, Manuela and Kleinpeter, Erich and Holdt, Hans-J{\"u}rgen}, title = {A novel polymeric disilver(I) complex containing both macrocyclic- and linear-coordinate silver(I) centres : [Ag-2(mn-15S(2)O(3))](infinity)(ClO4)(2 infinity) (mn-15S(2)O(3) = maleonitrile-dithia[15]crown-5)}, year = {1999}, language = {en} } @article{BalciKochKleinpeter2009, author = {Balci, Kubilay and Koch, Andreas and Kleinpeter, Erich}, title = {A theoretical IR spectroscopic study based on DFT calculations for free mn-15S(2)O(3) maleonitrile-dithiacrown ether compound}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2008.08.027}, year = {2009}, abstract = {The theoretically possible stable conformers of free mn-15S2O3 maleonitrile-dithiacrown ether molecule were searched by means of a conformational study which consists of molecular dynamics and energy minimization calculations performed with MM2 force field and successive geometry optimization + frequency calculations performed first at B3LYP/3- 21G and then at B3LYP/6-31G(d) levels of theory. The obtained calculation results have clearly indicated that the free molecule in electronic ground state is very flexible and accordingly has many possible stable conformers of different conformational properties at room temperature; among them, the one having a macrocyclic ring structure in which all of the ether units oriented toward the center of the ring was determined the energetically most preferable conformer. In addition, the equilibrium geometrical parameters, vibrational normal modes and associated IR spectral data of the determined most stable three conformers of the molecule were calculated at B3LYP/6-31+G(d) and B3LYP/6-31++G(d,p) levels of theory. A successful assignment of the fundamental bands observed in the recorded experimental solid phase and solution phase IR spectra of the molecule was achieved in the light of the theoretical data obtained from these DFT calculations. To fit the calculated harmonic wavenumbers to the experimental ones, two different scaling procedures, referred to as "Scaled Quantum Mechanical Force Field (SQM FF) methodology" and "Scaling wavenumbers with empirical dual scale factors", were proceeded independently.}, language = {en} } @article{KleinpeterKlod2004, author = {Kleinpeter, Erich and Klod, Sabrina}, title = {Ab initio calculation of the anisotropic/ring current effects of amino acid residues to locate the position of substrates in the binding site of enzymes}, year = {2004}, abstract = {The ring current effects of aromatic moieties and the anisotropic effects of the C=O and C-X (X = C, N, S) bonds and of the NH=C(NH2)-NH- moiety in the side chains of amino acid residues of proteins were ab initio calculated based on nuclear independent chemical shieldings as employed by P.v.R. Schleyer. Hereby, quantitative information about the spatial extension, sign and scope of the corresponding ring current/anisotropic effects was obtained and they were visualized as iso-chemical-shielding-surfaces. Examining this quantitative information compared with experimental NMR chemical shifts, the role of the corresponding amino acid residues in binding substrates in the binding site of enzymes was studied. (C) 2004 Elsevier B.V. All rights reserved}, language = {en} } @article{KochMikhovaKleinpeter2004, author = {Koch, Andreas and Mikhova, Bozhana and Kleinpeter, Erich}, title = {Ab initio MP2/GIAO/NBO study of the delta-syn-axial effect in C-13 NMR spectroscopy}, issn = {0022-2860}, year = {2004}, abstract = {The C-13 chemical shifts of 20 rigid bicyclic compounds have been calculated with ab initio HF and MP2 methods. The calculations showed very good reproducibility of the experimental values. The molecular orbital interactions in the rigid, nearly planar delta-syn-axial fragments in the isomeric groups of norbornane derivatives 1.x-4.x were studied in detail and were employed to explain the deshielding delta-syn-axial effect in C-13 NMR spectroscopy. (C) 2004 Elsevier B.V. All rights reserved}, language = {en} } @article{NeuvonenNeuvonenKochetal.2005, author = {Neuvonen, Helmi and Neuvonen, Kari and Koch, Andreas and Kleinpeter, Erich}, title = {Ab initio study of the substituent effects on the relative stability of the E and Z conformers of phenyl esters : Stereoelectronic effects on the reactivity of the carbonyl group}, issn = {1089-5639}, year = {2005}, abstract = {Equilibria between the Z (tau(1) = 0 degrees) and E (tau(1) = 180 degrees) conformers of p-substituted phenyl acetates 4 and trifluoroacetates 5 (X = OMe, Me, H, Cl, CN, NO2) were studied by ab initio calculations at the HF/6-31G* and MP2/6-31G* levels of theory. The preference for the Z conformer, Delta E(HF), was calculated to be 5.36 kcal mol(-1) and 7.50 kcal mot(-1) for phenyl acetate and phenyl trifluoroacetate (i.e., with X = H), respectively. The increasing electron-withdrawing ability of the phenyl substituent X increases the preference of the Z conformer. An excellent correlation with a negative slope was observed for both series between Delta E of the E-Z equilibrium and the Hammett sigma constant. By using an appropriate isodesmic reaction, it was shown that electron-withdrawing substituents decrease the stability of both conformers, but the effect is higher with the E conformer. Electron-withdrawing phenyl substituents decrease the delocalization of the lone pair of the ether oxygen to the C=O antibonding orbital (n(O) -> pi*(C=O)) in both the E and Z forms and in both series studied; this effect is higher in the E conformer than in the Z conformer. The n(O) -> pi*(C=O) electron donation has a minimum value with tau(1) = 90 degrees and a maximum value with tau(1) = 90 degrees (the Z conformer), the value with tau(1) = 180 degrees (the E conformer) being between these two values, obviously due to steric hindrance. The effects of the phenyl substituents on the reactivity of the esters studied are discussed in terms of molecular orbital interactions. ED/EW substituents adjust the availability of the pi*(C=O) antibonding orbital to interact with the lone pair orbital of the attacking nucleophile and therefore affect the reactivity: EW substituents increase and ED substituents decrease it. Excellent correlations were observed between the rate coefficients of nucleophilic acyl substitutions and pi*(C=O) occupancies of the ester series 4 and}, language = {en} } @article{KochKleinpeter1995, author = {Koch, Andreas and Kleinpeter, Erich}, title = {Ab-initio study and semiempirical calculations of keto-enol tautomerism of triazolopyrimidines}, year = {1995}, language = {en} } @article{KochThomasKleinpeter1997, author = {Koch, Andreas and Thomas, Steffen and Kleinpeter, Erich}, title = {Ab-initio study, semi-empirical calculation and NMR spectroscopy of keto-enol tautomerism of triazolopyrimidines}, year = {1997}, language = {en} } @article{OszczapowiczWawerDargatzetal.1995, author = {Oszczapowicz, J. and Wawer, I. and Dargatz, M. and Kleinpeter, Erich}, title = {Amidines .34. N-15 NMR spectra of trisubstituted amidines - substituent effects}, year = {1995}, language = {en} } @article{deAraujoChaconCarneiroetal.2010, author = {de Araujo, Martha T. and Chacon, Eluzir P. and Carneiro, Jos{\´e} W. de M. and Koch, Andreas and Kleinpeter, Erich}, title = {Analysis of anisotropic effects in trinuclear metal carbonyl compounds by visualization of through-space NMR shielding}, issn = {1610-2940}, doi = {10.1007/s00894-010-0662-3}, year = {2010}, abstract = {Through-space NMR shieldings were calculated for trinuclear metal-carbonyl compounds [M-3(CO)(12)] (M = Fe, Ru, Os), employing the nucleus-independent chemical shift approach. The through-space shieldings were visualized as a contour plot of iso-chemical shielding surfaces, and were applied to quantify the overall anisotropic effect of the carbonyl groups, as well as to identify the influence of the transition metal on the scopes of the corresponding anisotropy cones. The shielding surfaces show that the anisotropic effect of the carbonyl groups at equatorial positions changes depending on the metal. This effect was associated with pi-backdonation from the metal to the carbonyl groups in that position, in agreement with geometric data as well as calculated NMR parameters. Therefore, visualization of the through-space NMR shieldings of trinuclear metal-carbonyl compounds of group 8 is able to reflect the distinct arrangements of the carbonyl groups in these organometallic compounds.}, language = {en} } @article{KleinpeterKochSahooetal.2008, author = {Kleinpeter, Erich and Koch, Andreas and Sahoo, Himansu S. and Chand, Dillip Kumar}, title = {Anisotropic effect of the nitrate anion-manifestation of diamagnetic proton chemical shifts in the 1H NMR spectra of NO3-coordinated complexes}, doi = {10.1016/j.tet.2008.03.063}, year = {2008}, abstract = {The anisotropic effect of the planar nitrate anion NO3- has been ab initio calculated employing the Nucleus- Independent Chemical Shift (NICS) concept of von Ragu{\´e} Schleyer and visualized as Iso-Chemical-Shielding Surfaces (ICSSs) of various (de)shieldings. Complexation-induced shifts in the 1H NMR spectra of nitrate/metal complexes or nitrate/receptor supramolecules can be separated now into anisotropic influences of the suitably coordinated nitrate anions and effects originating from differential sources.}, language = {en} } @article{KleinpeterKriigerKoch2015, author = {Kleinpeter, Erich and Kriiger, Stefanie and Koch, Andreas}, title = {Anisotropy Effect of Three-Membered Rings in H-1 NMR Spectra: Quantification by TSNMRS and Assignment of the Stereochemistry}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {119}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {18}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.5b03078}, pages = {4268 -- 4276}, year = {2015}, abstract = {The spatial magnetic properties (through Space NAIR shieldings, TSNMRSs) of cyclopropane; of the heteroanalogous oxirane, thiirane, and aziridine; and of various substituted dis-, and tris-cyclic analogues have been computed by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSSs) of various size and direction. The TSNMRS values, thus obtained, can be employed to visualize the anisotropy (ring current) effect of I the cyclopropane ring moiety. This approach has been employed to qualify and quantify substituent influences and contributions of appropriate ring heteroatoms O, NH, and S on the anisotropy (ring current) effect of three-mernbered ring moieties, and to assign the stereochemistry of mono-, bis-, and tris cyclic structures containing cyclopropane as a structural element. Characteristic examples are included.}, language = {en} } @article{KihampaNkunyaJosephetal.2009, author = {Kihampa, Charles and Nkunya, Mayunga H. H. and Joseph, Cosam C. and Magesa, Stephen M. and Hassanali, Ahmed and Heydenreich, Matthias and Kleinpeter, Erich}, title = {Anti-mosquito and antimicrobial nor-halimanoids, isocoumarins and an anilinoid from Tessmannia densiflora}, issn = {0031-9422}, doi = {10.1016/j.phytochem.2009.07.024}, year = {2009}, abstract = {The nor-halimane diterpenoid tessmannic acid and its methyl, 2-methylisopropyl and 1-methylbutyl esters, the unusual isocoumarins 8-hydroxy-6-methoxy-3-pentylisocoumarin and 7-chloro-8-hydroxy-6-methoxy-3-pentylisocoumarin, and 5- pentyl-3-methoxy-N-butylaniline were isolated from the stem and root bark extracts of Tessmannia densiflora Harms (Caesalpiniaceae) that showed mosquito larvicidal activity. The structures were determined on interpretation of spectroscopic data. Tessmannic acid and its methyl ester exhibited antibacterial and antifungal activity. The compounds also caused high larvae and adult Anopheles gambiae mosquitoe mortality effects, and stronger mosquito repellency than that shown by the standard repellent DEET, hence indicating Tessmannia species to be potential sources of bioactive natural products.}, language = {en} } @article{KleinpeterKoch2012, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Antiaromaticity proved by the anisotropic effect in H-1 NMR Spectra}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {116}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {23}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/jp300860q}, pages = {5674 -- 5680}, year = {2012}, abstract = {The spatial magnetic properties (through-space NMR shieldings, or TSNMRSs) of the antiaromatic 9-oxaanthracene anion 12(-) and of the corresponding 9-dimeric dianion 11(2-) have been calculated by the gauge-invariant atomic orbitals (GIAO) perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSSs) of various size and direction. The TSNMRS values, thus obtained, can be employed to indicate antiaromaticity by paratropic ring currents of the anionic compounds of 11(2-) and 12(-) studied and other neutral and ionic antiaromatic molecules from previous studies because anisotropic effects of functional groups in H-1 NMR spectra have quantitatively proven to be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS).}, language = {en} } @article{KihampaNkunyaJosephetal.2010, author = {Kihampa, Charles and Nkunya, Mayunga H. H. and Joseph, Cosam C. and Magesa, Stephen M. and Hassanali, Ahmed and Heydenreich, Matthias and Kleinpeter, Erich}, title = {Antimosquito and antimicrobial clerodanoids and a chlorobenzoid from Tessmannia species}, issn = {1934-578X}, year = {2010}, abstract = {The clerodane diterpenoids trans-kolavenolic acid, 18-oxocleroda-3,13(E)-dien-15-oic acid, ent-(18- hydroxycarbonyl)-cleroda- 3,13(E)-dien-15-oate, 2-oxo-ent-cleroda-3,13(Z)-dien-15-oic acid and trans-2-oxo-ent-cleroda- 13(Z)-en-15-oic acid, and the chlorobenzenoid O-(3-hydroxy-4-hydroxycarbonyl-5-pentylphenyl)-3-chloro-4-methoxy-6-pentyl- 2-oxybenzoic acid were isolated from Tessmannia martiniana var pauloi and T. martiniana var matiniana. Structures were established based on interpretation of spectroscopic data. Some of the compounds exhibited significant antimosquito, antifungal and antibacterial activities.}, language = {en} } @inproceedings{MachumiYenesewMidiwoetal.2012, author = {Machumi, F. and Yenesew, Abiy and Midiwo, J. O. and Heydenreich, Matthias and Kleinpeter, Erich and Khan, S. and Tekwani, B. L. and Walker, L. A. and Muhammad, I}, title = {Antiparasitic and anticancer carvotacetone derivatives from Sphaeranthus bullatus}, series = {Planta medica : journal of medicinal plant and natural product research}, volume = {78}, booktitle = {Planta medica : journal of medicinal plant and natural product research}, number = {11}, publisher = {Thieme}, address = {Stuttgart}, issn = {0032-0943}, pages = {1201 -- 1202}, year = {2012}, language = {en} } @article{MachumiYenesewMidiwoetal.2012, author = {Machumi, Francis and Yenesew, Abiy and Midiwo, Jacob O. and Heydenreich, Matthias and Kleinpeter, Erich and Tekwani, Babu L. and Khan, Shabana I. and Walker, Larry A. and Muhammad, Ilias}, title = {Antiparasitic and anticancer carvotacetone derivatives of Sphaeranthus bullatus}, series = {Natural product communications : an international journal for communications and reviews}, volume = {7}, journal = {Natural product communications : an international journal for communications and reviews}, number = {9}, publisher = {NPC}, address = {Westerville}, issn = {1934-578X}, pages = {1123 -- 1126}, year = {2012}, abstract = {The CH2Cl2-MeOH (1:1) extract of the aerial parts of Sphaeranthus bullatus, an annual herb native to tropical East Africa, showed activity against chloroquine sensitive D6 (IC50 9.7 mu g/mL) and chloroquine resistant W2 (IC50 15.0 mu g/mL) strains of Plasmodium falciparum. Seventeen secondary metabolites were isolated from the extract through conventional chromatographic techniques and identified using various spectroscopic methods. The compounds were evaluated for their in vitro antiplasmodial, antileishmanial and anticancer activities revealing activity of four carvotacetone derivatives, namely 3-acetoxy-7-hydroxy-5-tigloyloxycarvotacetone (1) 3,7-dihydroxy-5-tigloyloxycarvotacetone (2), 3-acetoxy-5,7-dihydroxycarvotacetone (3) and 3,5,7-trihydroxycarvotacetone (4); with antiplasmodial IC50 values of 1.40, 0.79, 0.60 and 3.40 mu g/mL, respectively, against chloroquine sensitive D6 strains of P. falciparum; antiplasmodial activity of IC50 2.00, 0.90, 0.68 and 2.80 mu g/mL respectively, against chloroquine resistant W2 strains of P. falciparum, antileishmanial IC50, values of 0.70, 3.00, 0.70 and 17.00 mu g/mL, respectively, against the parasite L. donovanii promastigotes, and anticancer activity against human SK-MEL, KB, BT-549 and SK-OV-3 tumor cells, with IC50 values between <1.1 - 5.3 mu g/mL, for 1-3. In addition, cytotoxic effects of the active compounds were evaluated against monkey kidney fibroblasts (VERO) and pig kidney epithelial cells (LLC-PK11). The structures of carvotacetone derivatives were determined by ID and 2D NMR spectroscopy; the absolute stereochemical configuration of 3-acetoxy-7-hydroxy-5-tigloyloxycarvotacetone (I) was determined as 3R, 4R, 5S by circular dichroism, specific rotation, H-1 NMR and 2D NMR ROESY and NOESY experiments.}, language = {en} } @article{KleinpeterKochPihlaja2005, author = {Kleinpeter, Erich and Koch, Andreas and Pihlaja, Kalevi}, title = {Application of (1)J(C,H) coupling constants in conformational analysis}, issn = {0040-4020}, year = {2005}, abstract = {Conformational equilibria for a number of methyl substituted 1,3-dioxanes 1, 1,3-oxathianes 2 and 1,3-dithianes 3 were calculated at the HF and DFT levels of theory. In addition to the chair conformers also the energetically adjacent twist conformers were considered and the positions of the corresponding conformational equilibria estimated. On the basis of the global energy minima of conformers, participating in the conformational equilibria, the 1J(C,Hax,equ) coupling constants were calculated using the GIAO method and compared with the experimental values obtained from C-13, H- 1 coupled C-13 NMR spectra. The Perlin effect, the influence of the solvent and the suitability of this NMR parameter for assigning the conformational equilibria present are critically discussed. (c) 2005 Elsevier Ltd. All rights reserved}, language = {en} } @article{Kleinpeter2012, author = {Kleinpeter, Erich}, title = {Are lithium and sodium salts of N-(2-hydroxyphenyl)-salicylaldimine aromatic metalla-hetero[10]annulenes? An answer given by spatial magnetic properties (through space NMR shieldings-TSNMRS)}, issn = {1463-9076}, year = {2012}, abstract = {The spatial magnetic properties (through space NMR shieldings-TSNMRS) of the enol tautomer of N-(2- hydroxyphenyl)-salicylaldimine, the lithium and sodium salts in comparison with cyclodecapentaene and pyrano[2,3- b]pyrrole were studied to answer this question.}, language = {en} } @article{KleinpeterKoch2012, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Are lithium and sodium salts of N-(2-hydroxyphenyl)-salicylaldimine aromatic metalla-hetero[10]annulenes? An answer given by spatial magnetic properties (through space NMR shieldings-TSNMRS)}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {14}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {24}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c2cp40501f}, pages = {8742 -- 8746}, year = {2012}, abstract = {The spatial magnetic properties (through space NMR shieldings-TSNMRS) of the enol tautomer of N-(2-hydroxyphenyl)-salicylaldimine, the lithium and sodium salts in comparison with cyclodecapentaene and pyrano[2,3-b] pyrrole were studied to answer this question.}, language = {en} } @article{KleinpeterMichaelisKoch2015, author = {Kleinpeter, Erich and Michaelis, Marcus and Koch, Andreas}, title = {Are para-nitro-pyridine N-oxides quinonoid or benzenoid? An answer given by spatial NICS (TSNMRS)}, series = {Tetrahedron}, volume = {71}, journal = {Tetrahedron}, number = {15}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.02.043}, pages = {2273 -- 2279}, year = {2015}, abstract = {The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of a number of substituted para-nitro-pyridine N-oxides have been computed, visualized as Iso-Chemical-Shielding-Surfaces (ICSS) of various size and direction, and were examined subject to the present quinonoid or benzenoid pi-relectron distribution of the six-membered ring. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{KleinpeterHeydenreichShainyan2021, author = {Kleinpeter, Erich and Heydenreich, Matthias and Shainyan, Bagrat A.}, title = {At the experimental limit of the NMR conformational analysis}, series = {Organic letters}, volume = {23}, journal = {Organic letters}, number = {2}, publisher = {American Chemical Society}, address = {Washington}, issn = {1523-7060}, doi = {10.1021/acs.orglett.0c03878}, pages = {405 -- 409}, year = {2021}, abstract = {The low temperature (95 K) NMR study of 1-Ph-1-t-Bu-silacyclohexane (1) showed the conformational equilibrium to be extremely one-sided toward thePh(ax),t-Bueq conformer. The barrier to interconversion has been measured (4.2-4.6 kcal/mol) and the conformational equilibrium [Delta nu = 1990.64 ppm (Si-29), 618.9 ppm (C-13), 1-Ph-ax:1-Pheq = (95.6-96.6\%):(3.4-4.4\%), K = 25 +/- 3, Delta G degrees = -RT ln K = 0.58-0.63 kcal/mol] analyzed. The assignment and quantification of the NMR signals is supported by MP2 and DFT calculations.}, language = {en} } @article{KleinpeterKoch2020, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Bent Allenes or Di-1,3-betaines-An Answer Given on the Magnetic Criterion}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {124}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {16}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.0c01392}, pages = {3180 -- 3190}, year = {2020}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of bent allene 1, the corresponding C-extended 1,3-butadiene derivative 2, and a number of related compounds 3 -20 have been calculated using the gauge-independent atomic orbital perturbation method, employing the nucleus-independent chemical shift concept and visualized as isochemical shielding surfaces of various sizes and directions. Prior to that, both structures and C-13 chemical shifts were calculated and compared with available experimental bond lengths and delta(C-13)/ppm values (also, as a quality criterion for the computed structures). Bond lengths, the delta(C-13)/ppm, and the TSNMRS values are employed to qualify and quantify the electronic structure of the studied compounds in terms of dative or classical electron-sharing bonds.}, language = {en} } @article{KleinpeterKoch2019, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Benzenium Ion}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {123}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {20}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.9b03121}, pages = {4443 -- 4451}, year = {2019}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of the benzenium cation (C6H7+) 1 and of +/- I/M-substituted analogues C6H6X+ 3-8 [X = -Me, -CF3, -NH2, -NO2, -NO, -SiH3] have been calculated using the gauge-independent atomic orbital perturbation method employing the nucleus-independent chemical shift concept, and iso-chemical-shielding surfaces of various sizes and directions have been observed. The TSNMRS values were employed to compare the spatial magnetic properties (TSNMRS) of benzene and the benzenium ion 1 and then further compared with analogues 3-8, to answer the question whether the electronic structures of 1 and 3-8 are still similar to those of aromatic species or somewhat similar to the antiaromatic cyclopentadienyl cation 2, supported by structural data and delta(C-13)/ppm values.}, language = {en} } @article{KleinpeterKoch2019, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Benzyne - an acetylene- or cumulene-like electronic structure?}, series = {Tetrahedron}, volume = {75}, journal = {Tetrahedron}, number = {33}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2019.07.011}, pages = {4663 -- 4668}, year = {2019}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzyne 1 and analogues (benzene 2, 1,2,3-cyclohexatriene 3, cyclohexen-3-yne 4, cyclohexen-4-yne 5, cyclohexyne 6) have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values could be employed to compare the diatropic ring current effects of benzene and benzyne, and, when compared with the spatial magnetic properties of the analogues, to answer the question whether the benzyne electronic structure is more acetylene- or cumulene-like, supported by structural data and delta(C-13)/ppm values. (C) 2019 Published by Elsevier Ltd.}, language = {en} } @article{HausmannKassKlodetal.2004, author = {Hausmann, J. and Kass, S. and Klod, Sabrina and Kleinpeter, Erich and Kersting, Berthold}, title = {Binucleating aza-sulfonate and aza-sulfinate macrocycles : Synthesis and coordination chemistry}, issn = {1434-1948}, year = {2004}, abstract = {The preparation and ligating properties of S-oxygenated derivatives of a macrobinucleating hexaazadithiophenolate macrocycle H2L1 of the Robson type towards nickel(II) and zinc(II) ions are reported. Nickel complexes of the hexaazadiphenylsulfonate ligand (L-2)(2-)[(L-2)Ni-2(II)(mu-L)](+)(L = m-Cl-OBz(-) (3), Cl- (4) and OAc- (6)] are readily obtained in high yields by oxidation of the respective [(L-1)Ni-2(II)(mu-L)](+) parent complexes [L = m- Cl-OBz- (2), Cl- (1), OAc- (5)] with meta-chloroperoxybenzoic acid or hydrogen peroxide. Decomposition of the sulfonate complexes gives the free macrocycle H2L2 which, upon treatment with Zn(OAc)(2)(.)2H(2)O, produces the diamagnetic zinc complex [(L-2)Z(2)(II)(OAc)](+) (8). A dinuclear Cu-II complex of the hexaazadisulfinate derivative (L-3')(2-), [(L-3)CU2II](2+) (9), is formed rather unexpectedly by air oxidation of (L-1)(2-) in the presence of Cu-I. The crystal- structure determinations of the perchlorate or tetraphenylborate salts of 2, 3, and 4 show that the new ligands support the formation of binuclear complexes with bowl-shaped, calixarene-like binding cavities. NMR spectroscopic studies of 8 show that the complexes retain their solid-state structures in solution. A crystal-structure determination of 9 reveals two five-coordinate Cu-II ions bridged by the two sulfinate functions of (L-3)(2-)}, language = {en} } @article{YonedaLealSeidletal.2007, author = {Yoneda, Julliane Diniz and Leal, Katia Zaccur and Seidl, Peter Rudolf and Azeredo, Rodrigo Bagueira de V. and Kleinpeter, Erich}, title = {Camphor : a good model for illustrating NMR techniques}, year = {2007}, abstract = {CAMPHOR: A GOOD MODEL FOR ILLUSTRATING NMR TECHNIQUES. The use of Nuclear Magnetic Resonance spectroscopy to establish the three-dimensional structures of molecules is an important component of modern Chemistry courses. The combination of techniques that can be used for this purpose is conveniently illustrated by their application to the camphor molecule. This paper presents applications of several techniques used in NMR spectral interpretation in an increasing order of complexity. The result of individual experiments is illustrated in order to familiarize the user with the way connectivity through bonds and through space is established from 1D/2D-NMR spectra and molecular stereochemistry is determined from different NMR experiments}, language = {en} } @article{KoetzJagielskiKosmellaetal.2006, author = {Koetz, Joachim and Jagielski, Nicole and Kosmella, Sabine and Friedrich, Alwin and Kleinpeter, Erich}, title = {CdS nanocubes formed in phosphatidylcholin-based template phases}, volume = {288}, issn = {0927-7757}, doi = {10.1016/j.colsurfa.2006.01.013}, pages = {43 -- 1-3}, year = {2006}, abstract = {The paper is focused on the characterization and use of phosphatidylcholine (PC)-based inverse microemulsions as a template phase for the CdS nanoparticle formation. The optically clear, isotropic phase in the oil corner was identified as a "classical{\"o} water-in-oil microemulsion by means of NMR-diffusion measurements. Because of the very small dimensions of the water droplets, the isotropic phase shows a Newtonian-like flow behavior, and adequate amounts of bulk water cannot be detected by DSC. It is demonstrated that this w/o microemulsion can be used successfully as a nanoreactor for the formation of CdS nanoparticles with diameters of 4-5 nm. During the following process of solvent evaporation the individual small CdS nanoparticles aggregate to significant larger cubic nanoparticles, with an edge length of 2-40 nm, arranged in well-defined mosaic-like superstructures. In presence of SDS the nanocubes were stable up to 800 °C. It has to be stated here that polyelectrolytes prevent the formation of such well-ordered superstructures.}, language = {en} } @article{KleinpeterKoch2015, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Characterization and quantification of quasi-aromaticity by spatial magnetic properties (TSNMRS)}, series = {Tetrahedron}, volume = {71}, journal = {Tetrahedron}, number = {33}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.06.019}, pages = {5275 -- 5284}, year = {2015}, abstract = {The spatial magnetic properties (Through Space NMR Shieldings-TSNMRS) of various types of structures with suggested quasi-aromaticity (a summaring topic: in detail push pull, captodative, chelate, supramolecular aromaticity, etc.) have been computed, are visualized as Isochemical Shielding Surfaces (ICSS) of various size/direction and examined subject to identify and quantify present (partial) aromaticity. While the TSNMRS approach proves really helpful [even in cases of (4n+2) pi-electron cyclic moieties formed via non-covalent polar interactions] quasi-aromaticity suggested for enol forms of 1,3-dicarbonyl compounds via resonance-assisted intramolecular and intermolecular hydrogen bonding cannot be confirmed. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{KleinpeterKoch2011, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Chelatoaromaticity-existing: yes or no? An answer given by spatial magnetic properties (through space NMR shieldings-TSNMRS)}, issn = {1463-9076}, year = {2011}, language = {en} } @article{KleinpeterKoch2011, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Chelatoaromaticity-existing: yes or no? An answer given by spatial magnetic properties (through space NMR shieldings-TSNMRS)}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {46}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c1cp21942a}, pages = {20593 -- 20601}, year = {2011}, abstract = {The spatial magnetic properties (through space NMR shieldings-TSNMRS) of metal complexes (with ligands such as acetylacetone, 3-hydroxy-pyran(4) one) and "metallobenzenes" have been calculated by the GIAO perturbation method and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various sizes and directions. The TSNMRS values, thus obtained, can be successfully employed to quantify and visualize partial aromaticity of the metallocyclic ring by comparison with the spatial magnetic properties of the corresponding non-complexed ligands in comparable structural and electronic situations, and benzene, respectively. Because anisotropy/ring current effects in H-1 NMR spectra proved to be the molecular response property of TSNMRS, the results obtained concerning partial "chelatoaromaticity" are experimentally ensured.}, language = {en} } @article{KammKammSchmidtetal.2006, author = {Kamm, Birgit and Kamm, Michael and Schmidt, Matthias and Starke, Ines and Kleinpeter, Erich}, title = {Chemical and biochemical generation of carbohydrates from lignocellulose-feedstock (Lupinus nootkatensis) : quantification of glucose}, issn = {0045-6535}, doi = {10.1016/j.chemosphere.2005.03.073}, year = {2006}, abstract = {Different chemical and enzymatic methods were applied for the hydrolysis of main stems from Lupinus nootkatensis (harvest November 2002). The whole process (all steps) is based on the lignocellulose-feedstock biorefinery regime. The acid hydrolysis of L. was performed with concentrated hydrochloric acid; advantages in this process are exothermic hydrolysis and the possibility of acid recovery. Enzymatic hydrolysis achieved high yields of fermentable carbohydrates (regarding to input cellulose) with high selectivity. However, this way requires the generation of cellulose from L. by chemical pulping. Monosaccharide derivatives thus obtained were identified by their GC retention times and the corresponding MS fragmentation. Hexamethyldisilazane was used as derivatization reagent to prepare the trimethylsilyl derivatives of the carbohydrates and of the degradations products of cellulose from the different fractions. The glucose content was quantified by GC peak integration with respect to an internal standard.}, language = {en} } @article{BauerHartmannKleinpeteretal.2015, author = {Bauer, Monika and Hartmann, Lutz and Kleinpeter, Erich and Kuschel, Frank and Pithart, Cornelia and Weissflog, Wolfgang}, title = {Chiral Dopants Derived from Ephedrine/Pseudoephedrine: Structure and Medium Effects on the Helical Twisting Power}, series = {Molecular crystals and liquid crystals}, volume = {608}, journal = {Molecular crystals and liquid crystals}, number = {1}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {1542-1406}, doi = {10.1080/15421406.2014.949592}, pages = {14 -- 24}, year = {2015}, abstract = {Chiral dopants were obtained by acylation of enantiomerically pure ephedrine and pseudoephedrine with promesogenic carbonyl reagents. The products have been investigated with respect to their chiral transfer ability on nematic host matrices characterized by extreme differences of the dielectric anisotropy. It has been found that the medium dependence of the helicity induction nearly disappears at reduced temperatures. Based on variable temperature H-1 NMR studies on monoacylated homologues, the estimated coalescence temperatures and free activation enthalpies for the hindered rotation around C-N bonds could be correlated with the helical twisting power. Measurements by dielectric spectroscopy reveal the correlation between the molar mass of substituents linked to the chiral building block and the dynamic glass transition of corresponding chiral dopants. Furthermore, the effect of intramolecular and intermolecular hydrogen bonds has been studied by ATR-FTIR spectroscopy.}, language = {en} } @article{StarkeKammerGrunwaldetal.2008, author = {Starke, Ines and Kammer, Stefan and Grunwald, Nicolas and Schilde, Uwe and Holdt, Hans-J{\"u}rgen and Kleinpeter, Erich}, title = {Complexation of diazaperylene and bisisoquinoline with transition metal ions in the gas phase studied by electrospray ionization mass spectrometry}, year = {2008}, abstract = {The complex formation of the ligands 1,12-diazaperylene (dap), 1,1-bisisoquinoline (bis), 2,2-bipyridine (bpy) and 1,10-phenanthroline (phen) with transition metal ions (M = Fe, Co, Ni, Cu, Zn, Ru, Os, Re, Pd, Pt, Ag and Cd) in the gas phase has been studied by electrospray ionization mass spectrometry. With the exception of Ru, Os, Fe, Ni and Cu, singly charged complexes [MLn]+ (n = 1,2) were observed. The complexes of dap and bis with Ru, Os, Fe and Ni ions, and the mixed ligand complexes with bpy and phen, are preferably of the doubly charged type [ML3]2+. In addition, collision- induced dissociation (CID) measurements were employed to evaluate the relative stabilities of these complexes. The CID experiments of mixed-ligand complexes which contain both dap and phen or dap and bpy exhibit preferential elimination of bpy, indicating that bpy is a weaker ligand than phen and dap.}, language = {en} } @article{BoehmTomaszcikovaImrichetal.2009, author = {B{\"o}hm, Stanislav and Tomaszcikov{\´a}, Jana and Imrich, J{\´a}n and Danihel, Ivan and Kristian, Pavol and Koch, Andreas and Kleinpeter, Erich and Klika, Karel D.}, title = {Computational study to assign structure, tautomerism, E/Z and s-cis/s-trans isomerism, pi-delocalization, partial aromaticity, and the ring size of 1,3-thiazolidin-4-ones and 1,3-thiazin-4-ones formed from thiosemicarbazides}, issn = {0166-1280}, year = {2009}, abstract = {A set of structures encompassing 1-(9-acridinyl)thiosemicarbazide and its 2-methyl derivative together with their various tautomeric structures; the 5-membered ring 1,3-thiazolidin-4-one products resulting from the reaction of 1- (9-acridinyl)thiosemicarbazide and its 2-methyl derivative with dimethyl acetylenedicarboxylate (DMAD) together with the alternative 6-membered ring isomeric reaction products as well as other potential isomeric structures; and the 6- membered ring 1,3-thiazin-4-one product resulting from the reaction of 2-methyl-1-(9-acridinyl)thiosemicarbazide with methyl propiolate (MP) together with the alternative 5-membered ring isomeric reaction product were all extensively studied by molecular modeling calculations using DFT at the B3LYP/6-31G(d,p) level of theory. The ring-chain tautomerism of the thiosemicarbazides, the regio- and stereoselectivity of the reactions, the adopted conformations and E/Z configurations of the products, the prototropic tautomerism of all the compounds, and the reasons for the predominance of the s-cis conformation of the Z configuration of the 1,3-thiazolidin-4-one product in particular were all extensively analyzed. Comparison of the modeled structures were also made to the 1,3-thiazolidin-4-one and 1,3-thiazin-4-one structures of the methyl derivative as well as 1-(9-acridinyl)thiosemicarbazide available from X-ray crystallographic analysis. Tactics utilizing spectroscopic methods {IR frequencies (;) and NMR chemical shifts (;), scalar coupling constants (J), and NOEs (;)} in conjunction with molecular modeling calculations of the spectral parameters {frequency calculations (;) and NMR ; using the GIAO method and J by calculation of the Fermi contact term} were evaluated in terms of proving 5- or 6-membered ring formation.}, language = {en} } @article{BoehmTomašcikovaImrichetal.2009, author = {Boehm, Stanislav and Tomašcikov{\´a}, Jana and Imrich, J{\´a}n and Danihel, Ivan and Kristian, Pavol and Koch, Andreas and Kleinpeter, Erich and Klika, Karel D.}, title = {Computational study to assign structure, tautomerism, E/Z and s-cis/s-trans isomerism, pi-delocalization, partial aromaticity, and the ring size of 1,3-thiazolidin-4-ones and 1,3-thiazin-4-ones formed from thiosemicarbazides}, issn = {0166-1280}, doi = {10.1016/j.theochem.2009.09.019}, year = {2009}, abstract = {A set of structures encompassing 1-(9-acridinyl)thiosemicarbazide and its 2-methyl derivative together with their various tautomeric structures; the 5-membered ring 1,3-thiazolidin-4-one products resulting from the reaction of 1- (9-acridinyl)thiosemicarbazide and its 2-methyl derivative with dimethyl acetylenedicarboxylate (DMAD) together with the alternative 6-membered ring isomeric reaction products as well as other potential isomeric structures; and the 6- membered ring 1,3-thiazin-4-one product resulting from the reaction of 2-methyl-1-(9-acridinyl)thiosemicarbazide with methyl propiolate (MP) together with the alternative 5-membered ring isomeric reaction product were all extensively studied by molecular modeling calculations using DFT at the B3LYP/6-31G(d,p) level of theory. The ring-chain tautomerism of the thiosemicarbazides, the regio- and stereoselectivity of the reactions, the adopted conformations and E/Z configurations of the products, the prototropic tautomerism of all the compounds, and the reasons for the predominance of the s-cis conformation of the Z configuration of the 1,3-thiazolidin-4-one product in particular were all extensively analyzed. Comparison of the modeled structures were also made to the 1,3-thiazolidin-4-one and 1,3-thiazin-4-one structures of the methyl derivative as well as 1-(9-acridinyl)thiosemicarbazide available from X-ray crystallographic analysis. Tactics utilizing spectroscopic methods {1R frequencies (nu) and NMR chemical shifts (delta), scalar coupling constants (J), and NOEs (eta)} in conjunction with molecular modeling calculations of the spectral parameters (frequency calculations (v) and NMR 6 using the GIAO method and J by calculation of the Fermi contact term) were evaluated in terms of proving 5- or 6-membered ring formation.}, language = {en} } @article{KlinkaImrichDaniheletal.2005, author = {Klinka, Karel D. and Imrich, Jan and Danihel, I. and Bohm, Stanislav and Kristian, Pavol and Harnul'akova, S. and Pihlaja, Kalevi and Koch, Andreas and Kleinpeter, Erich}, title = {Configuration and E/Z interconversion mechanism of O(S)-allyl-S(O)-methyl-N-(acridin-9-yl)iminothiocarbonate}, issn = {0749-1581}, year = {2005}, abstract = {The configuration and dynamic behavior of O-allyl-S-methyl-N-(acridin-9-yl)iminothiocarbonate (1) and its S- allyl-O-methyl regioisomer (2) were studied using quantum chemical calculations and by applying a novel graphical method to scatter maps obtained from MD simulations for evaluation of an NOE-weighted internuclear distance (r(NOE)). Energy calculations indicated that the Z configuration was predominant for each compound and, further, this was supported both by the calculated chemical shifts and the rNOE. Both N-inversion- and rotation-type transition-state structures were also calculated for the E/Z isomerization process, the results indicating that the preferred interconversion mechanism for 1 is N-inversion, but contrastingly, interconversion via rotation is equally as probable as N-inversion for 2. This supports the notion that one or the other or both pathways can be active and each system needs to be assessed on a case- by-case basis. Copyright (c) 2005 John Wiley \& Sons, Ltd}, language = {en} } @article{KleinpeterHeydenreichWolleretal.1998, author = {Kleinpeter, Erich and Heydenreich, Matthias and Woller, Jochen and Wolf, Gunter and Koch, Andreas and Kempter, Gerhard and Pihlaja, Kalevi}, title = {Configuration and stereodynamics of exo/endoisomeric push-pull alkenes of pentadiene structure}, year = {1998}, language = {en} } @article{ShainyanKleinpeterSuslova2019, author = {Shainyan, Bagrat A. and Kleinpeter, Erich and Suslova, E. N.}, title = {Conformational Analysis of (1,1′-Phenyl-1,1′-silacyclohex-1-yl)disiloxane}, series = {Russian journal of general chemistry}, volume = {89}, journal = {Russian journal of general chemistry}, number = {4}, publisher = {Pleiades Publ.}, address = {New York}, issn = {1070-3632}, doi = {10.1134/S1070363219040121}, pages = {713 -- 716}, year = {2019}, abstract = {The DFT and MP2 theoretical conformational analysis of the recently synthesized (1,1-phenyl-1,1-silacyclohex-1-yl)disiloxane has revealed the energetic preference of the Ph-ax,Ph-ax conformer. The Ph-ax,Ph-ax: Ph-ax,Ph-eq: Ph-eq,Ph-eq conformers ratio has been estimated as of 46.6: 33.1: 20.3 from the M062X/6-311G(d,p) free energy simulation, suggesting the possibility of detecting individual conformers experimentally, e.g., by low-temperature H-1 and C-13 NMR spectroscopy. However, only the presence of several conformers has been detected by means of H-1 NMR spectroscopy at 113 K; determination of the (Hz) and G(\#) (kcal/mol) parameters for the 6-membered ring interconversion has been impossible due to the signals broadening at low temperature, signal temperature shifts, and extremely low barrier of ring inversion at T-c < 113 K.}, language = {en} } @article{KirpichenkoKleinpeterShainyan2010, author = {Kirpichenko, Svetlana V. and Kleinpeter, Erich and Shainyan, Bagrat A.}, title = {Conformational analysis of 3,3-dimethyl-3-silathiane, 2,3,3-trimethyl-3-silathiane and 2-trimethylsilyl-3,3- dimethyl-3-silathiane{\`u}preferred conformers, barriers to ring inversion and substituent effec}, issn = {0894-3230}, year = {2010}, abstract = {The first conformational analysis of 3-silathiane and its C-substituted derivatives, namely, 3,3-dimethyl-3- silathiane 1, 2,3,3-trimethyl-3-silathiane 2, and 2-trimethylsilyl-3,3-dimethyl-3-silathiane 3 was performed by using dynamic NMR spectroscopy and B3LYP/6-311G(d,p) quantum chemical calculations. From coalescence temperatures, ring inversion barriers ;G; for 1 and 2 were estimated to be 6.3 and 6.8;kcal/mol, respectively. These values are considerably lower than that of thiacyclohexane (9.4;kcal/mol) but slightly higher than the one of 1,1- dimethylsilacyclohexane (5.5;kcal/mol). The conformational free energy for the methyl group in 2 (;;G°;=;0.35;kcal/mol) derived from low-temperature 13C NMR data is fairly consistent with the calculated value. For compound 2, theoretical calculations give ;E value close to zero for the equilibrium between the 2-Meax and 2-Meeq conformers. The calculated equatorial preference of the trimethylsilyl group in 3 is much more pronounced (;;G°;=;1.8;kcal/mol) and the predominance of the 3-SiMe3 eq conformer at room temperature was confirmed by the simulated 1H NMR and 2D NOESY spectra. The effect of the 2-substituent on the structural parameters of 2 and 3 is discussed.}, language = {en} } @article{KleinpeterKirpichenkoUshakovetal.2011, author = {Kleinpeter, Erich and Kirpichenko, Svetlana V. and Ushakov, Igor A. and Shainyan, Bagrat A.}, title = {Conformational analysis of 3-methyl-3-silathiane and 3-fluoro-3-methyl-3-silathiane}, issn = {0894-3230}, year = {2011}, abstract = {The conformational equilibria of 3-methyl-3-silathiane 5, 3-fluoro-3-methyl-3-silathiane 6 and 1-fluoro-1- methyl-1-silacyclohexane 7 have been studied using low temperature 13C NMR spectroscopy and theoretical calculations. The conformer ratio at 103;K was measured to be about 5ax:5eq;=;15:85, 6ax:6eq;=;50:50 and 7ax:7eq;=;25:75. The equatorial preference of the methyl group in 5 (0.35;kcal;mol;1) is much less than in 3-methylthiane 9 (1.40;kcal;mol;1) but somewhat greater than in 1-methyl-1- silacyclohexane 1 (0.23;kcal;mol;1). Compounds 5-7 have low barriers to ring inversion: 5.65 (ax;;;eq) and 6.0 (eq;;;ax) kcal mol;1 (5), 4.6 (6), 5.1 (Meax;;;Meeq) and 5.4 (Meeq;;;Meax) kcal;mol;1 (7). Steric effects cannot explain the observed conformational preferences, like equal population of the two conformers of 6, or different conformer ratio for 5 and 7. Actually, by employing the NBO analysis, in particular, considering the second order perturbation energies, vicinal stereoelectronic interactions between the Si-X and adjacent C-H, C-S, and C-C bonds proved responsible.}, language = {en} } @article{KirpichenkoKleinpeterUshakovetal.2011, author = {Kirpichenko, Svetlana V. and Kleinpeter, Erich and Ushakov, Igor A. and Shainyan, Bagrat A.}, title = {Conformational Analysis of 3-Methyl-3-Silathiane and 3-Fluoro-3-Methyl-3-Silathiane}, series = {Journal of physical organic chemistry}, volume = {24}, journal = {Journal of physical organic chemistry}, number = {4}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0894-3230}, doi = {10.1002/poc.1758}, pages = {320 -- 326}, year = {2011}, abstract = {The conformational equilibria of 3-methyl-3-silathiane 5, 3-fluoro-3-methyl-3-silathiane 6 and 1-fluoro-1-methyl-1- silacyclohexane 7 have been studied using low temperature C-13 NMR spectroscopy and theoretical calculations. The conformer ratio at 103 K was measured to be about 5(ax):5(eq) - 15:85, 6(ax):6(eq)-50:50 and 7(ax):7(eq)-25:75. The equatorial preference of the methyl group in 5 (0.35 kcal mol(-1)) is much less than in 3-methylthiane 9 (1.40 kcal mol(-1)) but somewhat greater than in 1-methyl-1-silacyclohexane 1 (0.23 kcal mol(-1)). Compounds 5-7 have low barriers to ring inversion: 5.65 (ax -> eq) and 6.0 kcal mol(-1) (eq -> ax) (5), 4.6 kcal mol(-1) (6), 5.1 kcal mol(-1) (Me-ax -> Me-eq), and 5.4 kcal mol(-1) (Me-eq -> Me-ax) (7). Steric effects cannot explain the observed conformational preferences, like equal population of the two conformers of 6, or different conformer ratio for 5 and 7. Actually, by employing the NBO analysis, in particular, considering the second order perturbation energies, vicinal stereoelectronic interactions between the Si-X and adjacent C-H, C-S, and C-C bonds proved responsible.}, language = {en} } @article{ShainyanSuslovaKleinpeter2012, author = {Shainyan, Bagrat A. and Suslova, Elena N. and Kleinpeter, Erich}, title = {Conformational analysis of 4,4-dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane and 2,2,6,6-tetramethyl-4- (trifluoromethylsulfonyl)-1,4,2,6-oxazadisilinane}, year = {2012}, abstract = {4,4-Dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane 1 and 2,2,6,6-tetramethyl-4-(trifluoromethylsulfonyl)- 1,4,2,6-oxazadisilinane 2 were studied by variable temperature dynamic 1H, 13C, 19F NMR spectroscopy and theoretical calculations at the DFT (density functional theory) and MP2 (Moller-Plesset 2) levels of theory. Both kinetic (barriers to ring inversion) and thermodynamic data (frozen conformational equilibria) could be obtained for the two compounds. The computations revealed two minima on the potential energy surface for molecules 1 and 2 corresponding to the rotamers with the CF3SO2 group directed inward and outward the ring, the latter being 0.20.4 kcal/mol (for 1) and 1.1 kcal/mol (for 2) more stable than the former. The vibrational calculations at the DFT and MP2 levels of theory give the values of the free energy difference Delta G degrees for the 'inward' reversible arrow 'outward' equilibrium consistent with those determined from the experimentally measured ratio of the rotamers. The structure of crystalline compound 2 was ascertained by X-ray diffraction analysis.}, language = {en} } @article{ShainyanSuslovaKleinpeter2012, author = {Shainyan, Bagrat A. and Suslova, Elena N. and Kleinpeter, Erich}, title = {Conformational analysis of 4,4-dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane and 2,2,6,6-tetramethyl-4-(trifluoromethylsulfonyl)-1,4,2,6-oxazadisilinane}, series = {Journal of physical organic chemistry}, volume = {25}, journal = {Journal of physical organic chemistry}, number = {1}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0894-3230}, doi = {10.1002/poc.1882}, pages = {83 -- 90}, year = {2012}, abstract = {4,4-Dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane 1 and 2,2,6,6-tetramethyl-4-(trifluoromethylsulfonyl)-1,4,2,6-oxazadisilinane 2 were studied by variable temperature dynamic 1H, 13C, 19F NMR spectroscopy and theoretical calculations at the DFT (density functional theory) and MP2 (Moller-Plesset 2) levels of theory. Both kinetic (barriers to ring inversion) and thermodynamic data (frozen conformational equilibria) could be obtained for the two compounds. The computations revealed two minima on the potential energy surface for molecules 1 and 2 corresponding to the rotamers with the CF3SO2 group directed inward and outward the ring, the latter being 0.20.4 kcal/mol (for 1) and 1.1 kcal/mol (for 2) more stable than the former. The vibrational calculations at the DFT and MP2 levels of theory give the values of the free energy difference Delta G degrees for the 'inward' reversible arrow 'outward' equilibrium consistent with those determined from the experimentally measured ratio of the rotamers. The structure of crystalline compound 2 was ascertained by X-ray diffraction analysis.}, language = {en} } @article{KleinpeterShainyanSuslova2011, author = {Kleinpeter, Erich and Shainyan, Bagrat A. and Suslova, Elena N.}, title = {Conformational analysis of 4,4-dimethyl-4-silathiane and its S-oxides}, year = {2011}, language = {en} } @article{HolzbergerHoldtKleinpeter2004, author = {Holzberger, Anja and Holdt, Hans-J{\"u}rgen and Kleinpeter, Erich}, title = {Conformational analysis of mixed oxathia crown ethers and their complexational ability towards Ag(I) and Pd(II) : an experimental solution NMR and theoretical molecular modelling study}, issn = {1477-0520}, year = {2004}, abstract = {Both the conformation and flexibility of four mixed oxathia crown ethers and their Ag(I) and Pd(II) complexes were studied by H-1 NMR (delta, J, NOE, T-1), C-13 NMR, dynamic 1H NMR spectroscopy and molecular modelling. The stoichiometry and stability constants of the complexes were determined from corresponding Job's plots in the case of Ag(I) complexes as the interchange between free and complexed states was fast on the NMR timescale; interchange for the Pd(II) complexes was sufficiently slow such that distinct sub-spectra were observable for the free and complexed states. In all cases where complexation was observed, 1 : 1 complexes were formed. Global minima structures determined from the modelling studies were analysed with respect to the barriers to ring interconversion, the flexibility of the species in solution and the preferred complexation of Ag(I) and Pd(II) to the sulfur atoms of the crown ethers}, language = {en} } @article{KleinpeterShainyanSuslova2011, author = {Kleinpeter, Erich and Shainyan, Bagrat A. and Suslova, Elena N.}, title = {Conformational analysis of N-phenyl- and N-trifyl-4,4-dimethyl-4-silathiane 1-sulfimides}, issn = {0894-3230}, year = {2011}, language = {en} } @article{ShainyanSuslovaKleinpeter2011, author = {Shainyan, Bagrat A. and Suslova, Elena N. and Kleinpeter, Erich}, title = {Conformational analysis of N-phenyl- and N-trifyl-4,4-dimethyl-4-silathiane 1-sulfimides}, series = {Journal of physical organic chemistry}, volume = {24}, journal = {Journal of physical organic chemistry}, number = {8}, publisher = {Wiley-Blackwell}, address = {Malden}, issn = {0894-3230}, doi = {10.1002/poc.1811}, pages = {698 -- 704}, year = {2011}, abstract = {N-Substituted 4,4-dimethyl-4-silathiane 1-sulfimides Me2Si(sic)S=NSO2R [R- Ph (1), CF3 (2)] were studied experimentally by variable temperature dynamic NMR spectroscopy. Low temperature 13 C NMR spectra of the two compounds revealed the frozen ring inversion process and approximately equal content of the axial and equatorial conformers. Calculations of the 4-silathiane derivatives 1, 2 and the model compound [R Me (3)] as well as their carbon analogs, the similarly N-substituted (sic)S=NSO2R thiane 1-sulfimides [R = Ph (4), CF3 (5), Me (6)] at the DFT/B3LYP/6-311G(d, p) level in the gas phase and in chloroform solution using the PCM model at the same level of theory showed a strong dependence of the relative stability of the conformer on the solvent. The electronegative trifluoromethyl group increases the relative stability of the axial conformer.}, language = {en} } @article{Kleinpeter1998, author = {Kleinpeter, Erich}, title = {Conformational analysis of saturated six-membered oxygen-containing heterocyclic rings}, year = {1998}, language = {en} } @article{Kleinpeter1995, author = {Kleinpeter, Erich}, title = {Conformational analysis of six-membered sulfur-containing heterocycles}, year = {1995}, language = {en} } @article{HeydenreichKochRistauetal.1998, author = {Heydenreich, Matthias and Koch, Andreas and Ristau, Thomas and Knoll, Susanne and Heinicke, Jochen and Sieler, Joachim and Niemitz, Matthias and M{\"u}hlst{\"a}dt, Manfred and Kleinpeter, Erich}, title = {Conformational analysis of sulfur-containing heterocycles ; part I: synthesis and structural determination of diastereomerically pure 4,6-bis(phenoxymethyl)-1,2,5-trithiepanes}, year = {1998}, language = {en} } @article{KleinpeterGrotjahnKlinkaetal.2001, author = {Kleinpeter, Erich and Grotjahn, Manuela and Klinka, Karel D. and Drexler, Hans-Joachim and Holdt, Hans-J{\"u}rgen}, title = {Conformational and complexational study of some maleonitrile mixed oxadithia crown ethers by NMR spectroscopy and molecular modelling}, year = {2001}, abstract = {The macrocyclic ring interconversion of four maleonitrile mixed oxadithia crown ethers of variable ring size, mn-12-S2O2, mn-15-S2O3, mn-18-S2O4 and fn-12-S2O2, were studied by 1H and 13C NMR spectroscopy and by molecular modelling. The barriers to ring interconversion were estimated using variable temperature NMR spectroscopy and from the calculated activation energies, together with the spin-lattice relaxation times of the CH2 carbon atoms, conclusions were drawn regarding the intramolecular flexibility of the crown ethers in both the free state as well as the complexed state incorporating either AgI, BiIII, SbIII, PdII or PtII metal cations. Furthermore, both the stoichiometry of the complexes and the coordination sites of the crown ethers to the various cations were also clearly implicated. Molecular modelling was also utilised to ascertain the preferred conformers of the four compounds and their corresponding complexes, the results of which corroborated the experimental NMR results to a high degree.}, language = {en} } @article{GrotjahnKleinpeter1999, author = {Grotjahn, Manuela and Kleinpeter, Erich}, title = {Conformational behaviour of N-tosyl-substituted diaza-crown ethers}, year = {1999}, language = {en} } @article{ShainyanMoskalikHeydenreichetal.2014, author = {Shainyan, Bagrat A. and Moskalik, Mikhail Yu and Heydenreich, Matthias and Kleinpeter, Erich}, title = {Conformational equilibrium and dynamic behavior of bis-N-triflyl substituted 3,8-diazabicyclo[3.2.1]octane}, series = {Magnetic resonance in chemistry}, volume = {52}, journal = {Magnetic resonance in chemistry}, number = {8}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0749-1581}, doi = {10.1002/mrc.4086}, pages = {448 -- 452}, year = {2014}, abstract = {Restricted rotation about the N-S partial double bonds in a bis-N-triflyl substituted 3,8-diazabicyclo[3.2.1]octane derivative 1 has been frozen at low temperature (Delta G* = 11.6 kcal mol(-1)), and the existence of all four rotamers about the two N-S bonds, 3-in, 8-in, 3-in, 8-out, 3-out, 8-in, and 3-out, 8-out, respectively, proved experimentally by NMR spectroscopy and theoretically by DFT and MP2 calculations. Copyright (C) 2014 John Wiley \& Sons, Ltd.}, language = {en} } @article{ShainyanKleinpeter2014, author = {Shainyan, Bagrat A. and Kleinpeter, Erich}, title = {Conformational flexibility of 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline and its monoheterocyclic analogs}, series = {Russian journal of general chemistry}, volume = {84}, journal = {Russian journal of general chemistry}, number = {7}, publisher = {Pleiades Publ.}, address = {New York}, issn = {1070-3632}, doi = {10.1134/S1070363214070135}, pages = {1325 -- 1329}, year = {2014}, abstract = {Conformational behavior of the first cyclic organosilicon vinylsulfide, 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline as well as its monoheterocyclic analogs, 3,4-dihydro-2H-pyran, 3,4-dihydro-2H-thiopyran, and 1,1-dimethyl-1,2,3,4-tetrahydrosiline is studied in comparison with the carbocyclic analog, cyclohexene, using the methods of low-temperature NMR spectroscopy and theoretical calculations at the DFT and MP2 levels of theory. The barrier to the ring inversion with respect to that in cycloxene is increased in 3,4-dihydro-2H-pyran and 1,1-dimethyl-1,2,3,4-tetrahydrosiline, but, in contrast to the suggestions made in the literature, is decreased in 3,4-dihydro-2H-thiopyran. In 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline the barrier is intermediate between those in the corresponding monoheterocycles, 1,1-dimethyl-1,2,3,4-tetrahydrosiline and 3,4-dihydro-2H-thiopyran. The observed variations are rationalized from the viewpoint of the interaction of the pi-electrons of the C=C double bond with the orbitals of heteroatoms in the ring. The structure of the transition state for the ring inversion is discussed.}, language = {en} } @article{WackerDahmsSengeetal.2007, author = {Wacker, Philipp and Dahms, Katja and Senge, Mathias O. and Kleinpeter, Erich}, title = {Conformational Landscape of meso-(1,3-Dithian-2-yl)porphyrins}, doi = {10.1021/Jo0708700}, year = {2007}, abstract = {An investigation of the conformational landscape of 1,3-dithian-2-yl bearing porphyrins and the rotational behavior of the dithianyl substituents in meso position was carried out by variable-temperature (VT) NMR spectroscopy. Additionally, theoretical results for alternative conformations and energy barriers were obtained by molecular modeling. The study revealed different NH trans tautomers with regard to the orientation of the dithianyl ligands for the free base porphyrins 1-3. Relatively ruffled porphyrin core conformations were established for the transition states of the dithianyl rotation, resulting in a lower rotational energy barrier for the nickel(II) complex 4 compared to that of the free base systems. The data obtained and the first depiction of a rotational transition state for the rotation of bulky meso-alkyl substituents illustrate the close structural interplay between meso-alkyl substituents and the macrocycle conformation in porphyrins.}, language = {en} } @article{ShainyanKleinpeter2012, author = {Shainyan, Bagrat A. and Kleinpeter, Erich}, title = {Conformational preferences of Si-Ph,H and Si-Ph,Me silacyclohexanes and 1,3-thiasilacyclohexanes : Additivity of conformational energies in 1,1-disubstituted heterocyclohexanes}, issn = {0040-4020}, year = {2012}, abstract = {The conformational equilibria of 1-phenyl-1-silacyclohexane 1, 3-phenyl-1,3-thiasilacyclohexane 2, 1-methyl-1- phenyl-1-silacyclohexane 3, and 3-methyl-3-phenyl-1,3-thiasilacyclohexane 4 have been studied for the first time by low temperature C-13 NMR spectroscopy at 103 K. Predominance of the equatorial conformer of compound 1 (Ph-eq/Ph-ax=78\%:22\%) is much less than in its carbon analog, phenylcyclohexane (nearly 100\% of Ph-eq). And in contrast to 1-methyl-1- phenylcyclohexane, the conformers with the equatorial Ph group are predominant for compounds 3 and 4: at 103 K, Ph-eq/Ph- ax ratios are 63\%:37\% (3) and 68\%:32\% (4). As the Si-C bonds are elongated with respect to C-C bonds, the barriers to ring inversion are only between 5.2-6.0 (ax -> eq) and 5.4-6.0 (eq -> ax) kcal mol(-1). Parallel calculations at the DFT and MP2 level of theory (as well as the G2 calculations for compound 1) show qualitative agreement with the experiment. The additivity/nonadditivity of conformational energies of substituents on cyclohexane and silacyclohexane derivatives is analyzed. The geminally disubstituted cyclohexanes containing a phenyl group show large deviations from additivity, whereas in 1-methyl-1-phenyl-1-silacyclohexane and 3-methyl-3-phenyl-1,3-thiasilacyclohexane the effects of the methyl and phenyl groups are almost additive. The reasons for the different conformational preferences in carbocyclic and heterocyclic compounds are analyzed using the homodesmotic reactions approach.}, language = {en} } @article{ShainyanKleinpeter2012, author = {Shainyan, Bagrat A. and Kleinpeter, Erich}, title = {Conformational preferences of Si-Ph,H and Si-Ph,Me silacyclohexanes and 1,3-thiasilacyclohexanes. Additivity of conformational energies in 1,1-disubstituted heterocyclohexanes}, series = {Tetrahedron}, volume = {68}, journal = {Tetrahedron}, number = {1}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2011.10.082}, pages = {114 -- 125}, year = {2012}, abstract = {The conformational equilibria of 1-phenyl-1-silacyclohexane 1, 3-phenyl-1,3-thiasilacyclohexane 2, 1-methyl-1-phenyl-1-silacyclohexane 3, and 3-methyl-3-phenyl-1,3-thiasilacyclohexane 4 have been studied for the first time by low temperature C-13 NMR spectroscopy at 103 K. Predominance of the equatorial conformer of compound 1 (Ph-eq/Ph-ax=78\%:22\%) is much less than in its carbon analog, phenylcyclohexane (nearly 100\% of Ph-eq). And in contrast to 1-methyl-1-phenylcyclohexane, the conformers with the equatorial Ph group are predominant for compounds 3 and 4: at 103 K, Ph-eq/Ph-ax ratios are 63\%:37\% (3) and 68\%:32\% (4). As the Si-C bonds are elongated with respect to C-C bonds, the barriers to ring inversion are only between 5.2-6.0 (ax -> eq) and 5.4-6.0 (eq -> ax) kcal mol(-1). Parallel calculations at the DFT and MP2 level of theory (as well as the G2 calculations for compound 1) show qualitative agreement with the experiment. The additivity/nonadditivity of conformational energies of substituents on cyclohexane and silacyclohexane derivatives is analyzed. The geminally disubstituted cyclohexanes containing a phenyl group show large deviations from additivity, whereas in 1-methyl-1-phenyl-1-silacyclohexane and 3-methyl-3-phenyl-1,3-thiasilacyclohexane the effects of the methyl and phenyl groups are almost additive. The reasons for the different conformational preferences in carbocyclic and heterocyclic compounds are analyzed using the homodesmotic reactions approach.}, language = {en} } @article{ShainyanKirpichenkoKleinpeter2017, author = {Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Kleinpeter, Erich}, title = {Conformational Preferences of the Phenyl Group in 1-Phenyl-1-X-1-silacyclo-hexanes (X = MeO, HO) and 3-Phenyl-3-X-3-silatetrahydropyrans (X = HO, H) by Low Temperature C-13 NMR Spectroscopy and Theoretical Calculations}, series = {The journal of organic chemistry}, volume = {82}, journal = {The journal of organic chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.7b02505}, pages = {13414 -- 13422}, year = {2017}, abstract = {New Si-phenyl-substituted silacyclohexanes and 3-silatetrahydropyrans have been synthesized and studied with respect to the conformational equilibria of the heterosix-membered ring by low temperature C-13 NMR spectroscopy and quantum chemical calculations. For 1-methoxy-1-phenylsilacyclohexane 1 and 3-phenyl-3-silatetrahydropyran 4 the conformational equilibria could be frozen and assigned. The Ph-ax reversible arrow Ph-eq equilibrium constants at 103 K are 2.21 for 1 and 4.59 for 4. In complete agreement with former studies of similar silicon compounds, molecules 1 and 4 prefer to adopt the Pheq conformation. The conformational equilibria of 1-hydroxy-1-phenylsilacydohexane 2 and 3-hydroxy-3-phenyl-3-silatetrahydropyran 3 could not be frozen at 100 K and proved to be heavily one-sided (if not anancomeric). Obviously, there is a general trend of predominance of Phax conformer in the gas phase and of Pheq in solution. For the isolated molecules of silanols 2 and 3, calculations allowed to explain the axial predominance of the phenyl group by a larger polarization of the Si-Ph than of the Si-O bond in the Phax conformer and additional destabilization of 3-Ph-eq conformer by repulsion of unidirectional dipoles of the endocyclic oxygen lone pair and of the highly polar axial Si-O bond.}, language = {en} } @article{KochStarkeKleinpeter1995, author = {Koch, Andreas and Starke, Ines and Kleinpeter, Erich}, title = {Conformational study of Dibenzo crown ethers and their complexation with Li+ and Na+}, year = {1995}, language = {en} } @article{KovacsTothKleinpeteretal.2003, author = {Kovacs, J. and Toth, G. and Kleinpeter, Erich and Schilde, Uwe}, title = {Crystal structure of trans, cis-({\~n})-3{\"i}-4-fluorophenyl)-2-phenylspiro[2H-1-benzothiopyran-34H,2{\"i}-oxiran]-4-one 1- oxide, C22H15FO3S}, issn = {1433-7266}, year = {2003}, language = {en} } @article{KleinpeterKoch2022, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Cyclazines-structure and aromaticity or antiaromaticity on the magnetic criterion}, series = {European journal of organic chemistry}, volume = {2022}, journal = {European journal of organic chemistry}, number = {8}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.202101362}, pages = {12}, year = {2022}, abstract = {Structure and spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of all ten cycl[2.2.2]azine to cycl[4.4.4]azine, hetero-analogues and the corresponding hydrocarbons have been calculated at the B3LYP/6-311G(d,p) theory level using the GIAO perturbation method and employing the nucleus independent chemical shift (NICS) concept. The TSNMRS values (actually, the ring current effect as measurable in H-1 NMR spectroscopy) are visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction, and employed to readily qualify and quantify the degree of (anti)aromaticity. Results are confirmed by NMR [delta(H-1)/ppm, delta(N-15)/ppm] and geometry (planar, twisted, bow-shaped) data. The cyclazines N[2.2.2](-) up to N[2.4.4](-) are planar or at most slightly bowl-shaped and, due to coherent peripheral ring currents (except in N[2.3.3](-), N[2.3.4], N[3.3.4](+) and N[2.4.4](+)), develop aromaticity or anti-aromaticity of the whole molecules dependent on the number of peripheral conjugated pi electrons. The cyclazines N[2.3.3](-), N[2.3.4], N[3.3.4](+) and N[2.4.4](+) develop two ring currents of different direction within the same molecule, in which the dominating ring current proves to be paratropic (in N[3.3.4](+) diatropic) including the nodal N p(z) lone pair into the conjugation. The residual cyclazines N[3.4.4], N[4.4.4](-) and N[4.4.4](+) are heavily twisted and, therefore, are not developing peripheral or diverse ring currents. The TSNMRS information about cyclazines and the parent tricyclic annulene analogues is congruent subject to structure and number of peripheral or internal conjugated pi electrons, the corresponding (anti)aromaticity is in unequivocal accordance with Huckel's rule.}, language = {en} } @article{KleinpeterKochShainyan2008, author = {Kleinpeter, Erich and Koch, Andreas and Shainyan, Bagrat A.}, title = {Cyclobutadiene dianion derivatives : Planar 4c,6e or three-dimensional 6c,6e aromaticity?}, doi = {10.1016/j.theochem.2008.05.027}, year = {2008}, abstract = {The spatial magnetic properties (Through Space NMR Shieldings - TSNMRS) of two cyclobutadiene derivatives (2 and 5) and of a number of cyclobutadiene dianion derivatives (3, 4 and 6-8) have been calculated by the GIAO perturbation method employing the Nucleus-Independent Chemical Shift (NICS) concept of P. v. Ragu{\´e} Schleyer, and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various size and direction. TSNMRS values can be successfully employed to quantify and visualize the (anti)aromaticity of the compounds studied and to discuss the influence of Li+ complexation to cyclobutadiene dianion (4a, 7 and 8) on planar 4c,6e or three-dimensional 6c,6e aromaticity.}, language = {en} } @article{KleinpeterKoch2021, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Dative or coordinative carbon-boron bond in boron trapped N-heterocyclic carbenes (NHCs)?}, series = {Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry}, volume = {80}, journal = {Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0040-4020}, doi = {10.1016/j.tet.2020.131787}, pages = {8}, year = {2021}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of isolated as well as B-C bond length varied model compounds (BR3 trapped NHCs) have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the present dative vs. coordinative bond character of the boron-carbon bond in the trapped NHCs. Results are confirmed by bond lengths and B-11/C-13 chemical shift variations in the BR3 trapped NHCs.}, language = {en} } @article{BaranacStojanovicKochKleinpeter2012, author = {Baranac-Stojanovic, Marija and Koch, Andreas and Kleinpeter, Erich}, title = {Density Functional Calculations of the Anisotropic Effects of Borazine and 1,3,2,4-Diazadiboretidine}, series = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, volume = {13}, journal = {ChemPhysChem : a European journal of chemical physics and physical chemistry}, number = {17}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1439-4235}, doi = {10.1002/cphc.201200732}, pages = {3803 -- 3811}, year = {2012}, abstract = {On the basis of the nucleus-independent chemical shift (NICS) concept, the anisotropic effects of two inorganic rings, namely, borazine and planar 1,3,2,4-diazadiboretidine, are quantitatively calculated and visualized as isochemical shielding surfaces (ICSSs). Dissection of magnetic shielding values along the three Cartesian axes into contributions from s and p bonds by the natural chemical shieldingnatural bond orbital (NCSNBO) method revealed that their appearance is not a simple reflection of the extent of (anti)aromaticity.}, language = {en} } @article{KlikaKramerKleinpeter2009, author = {Klika, Karel D. and Kramer, Markus and Kleinpeter, Erich}, title = {DFT computational studies of hydrogen bonding-based diastereomeric complexes : limitations and applications to enantiodifferentiation}, issn = {0166-1280}, doi = {10.1016/j.theochem.2009.08.003}, year = {2009}, abstract = {Molecular modeling calculations using DFT at the B3LYP/6-31G(d,p) level of theory have been performed on diastereomeric complexes formed between chiral carboxylate anions and chiral urea receptors, a combination previously demonstrated to enable enantiodifferentiation by electrochemical sensing. The calculations correctly predicted the stability order of the enantiomers in acetonitrile solution when the distinction between the enantiomers was above the declared threshold reliability value of 1 kcal mol;1 for computations at this level of theory. Thus, the calculations can not only be applied to predict the likely success of undertakings using the analytical method, it can also, provided ;E is sufficient, potentially be used to determine the absolute configuration of chiral analytes with at least the racemate in hand. The previously successful enantiodifferentiations of various amino acids and alcohols using chiral ion mobility spectroscopy (CIMS) with (S)-2-butanol as the chiral selector were also evaluated by DFT calculations. The calculations again correctly predicted the stability order of the enantiomers when the calculated ;E was above the threshold value though cases not providing a value for ;E above the threshold value was problematic for this system. Attempts to address this shortcoming included an expanded conformational evaluation, a broader analytical approach, and an extended basis set.}, language = {en} } @article{NeuvonenNeuvonenKochetal.2007, author = {Neuvonen, Helmi and Neuvonen, Kari and Koch, Andreas and Kleinpeter, Erich}, title = {DFT study of the substituent cross-interaction effects on the conformation of substituted N-benzylideneanilines : Models of liquid crystal forming compounds ; use of C-13 Nmr chemcal shift of the C=N carbon as a tool to predict the conformation of the molecule}, doi = {10.1016/j.theochem.2007.03.023}, year = {2007}, abstract = {The conformations of N-benzylideneani lines p-X-C6H4-CH=N-C6H4 p-Y (X, Y = NO2, CN, CF3, F, Cl, Br, H, Me, OMe, NMe2) have been studied by B3LYP density functional (DFT) hybrid method in combination with the 6-31G* or 6-311G* split valence basis set. The twist of the plane of the aniline ring with respect to the other part of the molecule (tau(2)) is systematically controlled by substituents X and Y, the effect of Y being larger. The value of the dihedral angle tau(2), correlates nicely with equation tau(2) = rho(F)(Y)(x)sigma(F)(Y)+rho(+R)(Y)(x)sigma(+)(R)(Y) + k(x) or tau(2) = rho(F)(X)(y)sigma(F)(X)+rho(-)(R)(X)(y)sigma(+)(R)(X) + k(y), respectively, when aniline or benzylidene substituent is varied. ED substituents X diminish the sensitivity of tau(2) to the aniline substituent Y[rho(F)(Y)(x) and rho(+)(R)(Y)(x)] while ED substituents Y increase the sensitivity Of T2 to the benzylidene substituent X[rho(F)(X)(y) and rho(+)(R)(X)(y)]. There seems to be two competitive conjugative interactions for the aniline ring n electrons: one with the nitrogen lone pair and one with the C=N unit. Substituents X and Y adjust the extent of these interactions and therefore the conformation of the molecule. A good correlation is observed between the dihedral angle tau(2) and the experimental C-13 NMR chemical shift of the C=N carbon of N-benzylideneanilines in CDCl3 (C) 2007 Elsevier B.V. All rights reserved.}, language = {en} } @article{KleinpeterFrank2009, author = {Kleinpeter, Erich and Frank, Andrea}, title = {Distinction of Push,pull effect and steric hindrance in disubstituted alkynes}, issn = {0040-4020}, doi = {10.1016/j.tet.2009.03.075}, year = {2009}, abstract = {The push,pull effect in two series of disubstituted alkynes was studied at the DFT level [B3LYP/6-311G(d)] by application of the 13C chemical shift differences (GIAO) between the alkyne carbon atoms (Delta delta (C C)), the charge difference between these carbons (Delta q(C C)), the occupation quotient (NBO) of anti-bonding pi*, and bonding pi orbitals (pi*(C C)/pi(C C)) and the bond length (d(C C)) of the C C triple bond. The linear dependence of d(C C) versus pi*(C C)/pi(C C) quantifies changes in the push,pull effect while deviations from the latter correlation indicate and ascertain quantitatively to what extent steric hindrance restricts the strain-less conjugation of the C C triple bond pi- orbitals in the disubstituted alkynes.}, language = {en} } @article{ModarresiAlamKhamooshiRostamizadehetal.2007, author = {Modarresi-Alam, Ali Reza and Khamooshi, Ferydoon and Rostamizadeh, Mohsen and Keykha, Hossein and Nasrollahzahdeh, Mahmoud and Bijanzadeh, Hamid-Reza and Kleinpeter, Erich}, title = {Dynamic 1H NMR spectroscopic study of the restricted S-N rotation in aryl-N-(arylsulfonyl)-N- (triphenylphosphoranylidene)imidocarbamates}, year = {2007}, abstract = {Dynamic 1H NMR (500 MHz) investigation of aryl-N-(arylsulfonyl)-N-(triphenylphosphoranylidene)imidocarbamates in CDCl3, CD3COCD3, and CD3OD at the temperature range of 183-298 K is reported. The observed free energy barriers (almost 12 kcal mol;1) are attributed to conformational isomerization about the N{\`u}S bond and these barriers show very little solvent dependence.}, language = {en} } @article{ModarresiAlamAlsadatAmiraziziBagherietal.2009, author = {Modarresi-Alam, Ali Reza and Alsadat Amirazizi, Homeyra and Bagheri, Hajar and Bijanzadeh, Hamid-Reza and Kleinpeter, Erich}, title = {Dynamic 1H NMR spectroscopic study of the ring inversion in N-sulfonyl morpholines-studies on N-S interactions}, issn = {0022-3263}, year = {2009}, abstract = {The effect of the exocyclic conjugation, via d;p orbital interaction and/or negative hyperconjugation (anomeric effect) of the N;S bond, on the inversion of the morpholine ring in some N-arylsulfonyl morpholines is studied by variable-temperature 1H NMR spectroscopy in different solvents. The observed free energy barriers are 9.2;10.3 kcal mol;1; the lower values were obtained with increasing conjugation (substituents of higher electron withdrawing power) along the series. The barrier to ring inversion of 1e was solvent independent. X-ray data of compounds 1b,d reveal the chair conformation of the six-membered ring, the flattened pyramidal orientation of the ring nitrogen atom, and the sulfonyl group in equatorial position with the plane containing the Caryl;S;N bond perpendicular to the plane of the benzene ring. In addition, the sulfonamide group prefers a conformation with the S;C bond antiperiplanar with respect to the nitrogen atom lone pair and the ;CH2;N;CH2; moieties in staggered conformation with the S;O bonds of the SO2 group.}, language = {en} } @article{ModarresiNajafiRostamizadehetal.2007, author = {Modarresi, Ali Reza and Najafi, Parisa and Rostamizadeh, Mohsen and Keykha, Hossein and Bijanzadeh, Hamid-Reza and Kleinpeter, Erich}, title = {Dynamic 1H NMR study of the barrier to rotation about the C-N bond in primary carbamates and its solvent dependence}, year = {2007}, abstract = {The dynamic 1H NMR study of some primary carbamates in the solvents CDCl3 and CD3COCD3 between 183 and 298 K is reported. The free energies of activation, thus obtained (12.4 to 14.3 kcal mol-1), were attributed to the conformational isomerization about the N-C bond. These barriers to rotation show solvent dependence in contrast to the tertiary analogues and are lower in free energy by ca. 2-3 kcal mol-1.}, language = {en} } @article{ModarresiAlamAmiraziziBagherietal.2009, author = {Modarresi-Alam, Ali Reza and Amirazizi, Homeyra Alsadat and Bagheri, Hajar and Bijanzadeh, Hamid-Reza and Kleinpeter, Erich}, title = {Dynamic H-1 NMR spectroscopic study of the ring inversion in N-sulfonyl morpholines : studies on N-S interactions}, issn = {0022-3263}, doi = {10.1021/Jo900454a}, year = {2009}, abstract = {The effect of the exocyclic conjugation, via d-p orbital interaction and/or negative hyperconjugation (anomeric effect) of the N-S bond, on the inversion of the morpholine ring in some N-arylsulfonyl morpholines is studied by variable-temperature H-1 NMR spectroscopy in different solvents. The observed free energy barriers are 9.2-10.3 kcal mol(-1); the lower values were obtained with increasing conjugation (substituents of higher electron withdrawing power) along the series. The barrier to ring inversion of le was solvent independent. X-ray data of compounds 1b,d reveal the chair conformation of the six-membered ring the flattened pyramidal orientation of the ring nitrogen atom, and the sulfonyl group in equatorial position with the plane containing the C-aryl-S-N bond perpendicular to the plane of the benzene ring. In addition, the sulfonamide group prefers a conformation with the S-C bond antiperiplanar with respect to the nitrogen atom lone pair and the -CH2-N-CH2- moieties in staggered conformation with the S-O bonds of the SO2 group.}, language = {en} } @article{MovahedifarModarresiAlamKleinpeteretal.2017, author = {Movahedifar, Fahimeh and Modarresi-Alam, Ali Reza and Kleinpeter, Erich and Schilde, Uwe}, title = {Dynamic H-1-NMR study of unusually high barrier to rotation about the partial C-N double bond in N,N-dimethyl carbamoyl 5-aryloxytetrazoles}, series = {Journal of molecular structure}, volume = {1133}, journal = {Journal of molecular structure}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2016.12.010}, pages = {244 -- 252}, year = {2017}, abstract = {The synthesis of new N,N-dimethyl carbamoyl 5-aryloxytetrazoles have been reported. Their dynamic H-1-NMR via rotation about C-N bonds in moiety of urea group [a; CO-NMe2 and b; (2-tetrazolyl)N-CO rotations] in the solvents CDCl3 (223-333 K) and DMSO (298-363 K) is studied. Accordingly, the free energies of activation, obtained 16.5 and 16.9 kcal mol(-1) respectively, attributed to the conformational isomerization about the Me2N-C=O bond (a rotation). Moreover, a and b barrier to rotations in 5-((4-methylphenoxy)-N,N-dimethyl-2H-tetrazole-2-carboxamide (P) also were computed at level of B3LYP using 6-311++G** basis set. The optimized geometry parameters are in good agreement with X-ray structure data. The computation of energy barrier for a and b was determined 16.9 and 2.5 kcal mol(-1), respectively. The former is completely in agreement with the result obtained via dynamic NMR. X-ray structure analysis data demonstrate that just 2-acylated tetrazole was formed in the case of 5-(p-tolyloxy)-N,N-dimethyl-2H-tetrazole-2-carboxamide. X-ray data also revealed a planar trigonal orientation of the Me2N group which is coplanar to carbonyl group with the partial double-bond C-N character. It also demonstrates the synperiplanar position of C=O group with tetrazolyl ring. On average, in solution the plane containing carbonyl bond is almost perpendicular to the plane of the tetrazolyl ring (because of steric effects as confirmed by B3LY12/6-311++G**) while the plane containing Me2N group is coplanar with carbonyl bond which is in contrast with similar urea derivatives and it demonstrates the unusually high rotational energy barrier of these compounds. (C) 2016 Elsevier B.V. All rights reserved.}, language = {en} } @article{HeydenreichKochKleinpeteretal.1997, author = {Heydenreich, Matthias and Koch, Andreas and Kleinpeter, Erich and Zimmermann, Thomas}, title = {Dynamic NMR study of the flexibility of 2-amino-3-aroyl-4,6-diaryl-pyrylium salts}, issn = {0937-0633}, doi = {10.1007/s002160050205}, year = {1997}, language = {en} } @article{Kleinpeter1995, author = {Kleinpeter, Erich}, title = {Effect of the variation of ring size of cyclic NR2 substituents on the barrier to rotation in amides, thioamides and related compounds}, year = {1995}, language = {en} }