@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 = {The anisotropic effect of functional groups in 1H NMR spectra is the molecular response property of spatial NICS-the frozen conformational equilibria of 9-arylfluorenes}, issn = {0040-4020}, year = {2011}, abstract = {Rotation about the single bond adjoining the aryl and fluorene moieties in 9-arylfluorenes can be frozen out on the NMR timescale if methyl groups are located at either one or both of the ortho positions of the aryl substituent. In the ground-state of these rotamers, the planes of the aryl and fluorene moieties are perpendicular to each other and the methyl protons are either shielded or deshielded, respectively, due to the ringe current effect of the fluorene moiety. This anisotropic effect on the 1H chemical shifts of the methyl protons has been quantified on the basis of through- space NMR shieldings (TSNMRS) and subsequently _______ compared with the experimentally observed chemical shift differences _____. In this context, the experimental anisotropic effects of functional groups in the !H NMR have proven to quantitatively be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS). Differences between _______ and _____ were, for the first time, also quantified as arising from steric compression.}, 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{KleinpeterHeydenreichKochetal.2012, author = {Kleinpeter, Erich and Heydenreich, Matthias and Koch, Andreas and Linker, Torsten}, title = {Synthesis and NMR spectroscopic conformational analysis of esters of 4-hydroxy-cyclohexanone-the more polar the molecule the more stable the axial conformer}, issn = {0040-4020}, year = {2012}, abstract = {The esters of 4-hydroxy-cyclohexanone and a series of carboxylic acids R-COOH with R of different electronic and steric influence (R=Me, Et, n-Pr, i-Pr, n-Bu, i-Bu, sec-Bu, t-Bu, CF3, CH2Cl, CHCl2, CCl3, CH2Br, CHBr2, and CBr3) were synthesized and the conformational equilibria studied by 1H and 13C NMR spectroscopy at 103 K and at 295 K, respectively. The geometry of optimized structures of the axial/equatorial chair conformers was computed at the ab initio MO and DFT levels of theory. Only one preferred conformation was obtained for the axial and the equatorial conformer as well. When comparing the conformational equilibria of the cyclohexanone esters with those of the corresponding cyclohexyl esters a certain polarity contribution of the cyclohexanone framework was revealed, which is independent of the substituent effects and increases the stability of the axial conformers by a constant amount.}, language = {en} } @article{KleinpeterShainyanKirpichenkoetal.2012, author = {Kleinpeter, Erich and Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Shlykov, Sergei A.}, title = {Structure and Conformational Properties of 1,3,3-Trimethyl-1,3-Azasilinane : Gas Electron Diffraction, Dynamic NMR, and Theoretical Study.}, issn = {1089-5639}, year = {2012}, language = {en} } @article{KleinpeterCsuetoertoekiSzatmarietal.2012, author = {Kleinpeter, Erich and Cs{\"u}t{\"o}rt{\"o}ki, Ren{\´a}ta and Szatm{\´a}ri, Istv{\´a}n and Koch, Andreas and Fulop, Ferenc}, title = {Syntheses and conformational analyses of new naphth[1,2-e][1,3]oxazino[3,2-c]quinazolin-13-ones}, year = {2012}, abstract = {The syntheses of naphth[1,2-e][1,3]oxazino[3,2-c]quinazolin-13-one derivatives (3a-f) were achieved by the solvent-free heating of benzyloxycarbonyl-protected intermediates (2a-f) with MeONa. For intermediates 2a-f, prepared by the reactions of substituted aminonaphthols with benzyl N-(2-formylphenyl)carbamate, not only the expected trans ring form B and chain form A1, but also the rearranged chain form A2 as a new tautomer were detected in DMSO at room temperature. The quantity of A2 in the tautomeric mixture was changed with time. Conformational analyses of the target heterocycles 3a-f by NMR spectroscopy and accompanying theoretical calculations at the DFT level of theory revealed that the oxazine ring preferred a twisted chair conformation and the quinazolone ring was planar. Besides the conformations, both the configurations at C-7a and C-15 and the preferred rotamers of the 1-naphthyl substituent at C-15 were assigned, which allowed evaluation of the aryl substituent-dependent steric hindrance in this part of the molecules. Configurational assignments were corroborated by quantifying the ring current effect of 15-aryl in terms of spatial NICS.}, language = {en} } @article{KleinpeterLammermannKuehn2011, author = {Kleinpeter, Erich and Lammermann, Anica and K{\"u}hn, Heiner}, title = {Synthesis and NMR spectra of the syn and anti isomers of substituted cyclobutanes-evidence for steric and spatial hyperconjugative interactions}, issn = {0040-4020}, year = {2011}, abstract = {The syn and anti isomers of cis,cis-tricyclo[5.3.0.0(2.6)]dec-3-ene derivatives have been synthesized and their (1)H and (13)C NMR spectra unequivocally analyzed. Both their structures and their (1)H and (13)C NMR chemical shifts were calculated by DFT, the latter two calculations employing the GIAO perturbation method. Additionally, calculated NMR shielding values were partitioned into Lewis and non-Lewis contributions from the bonds and lone pairs involved in the molecules by accompanying NBO and NCS analyses. The differences between the syn and anti isomers were evaluated with respect to steric and spatial hyperconjugation interactions.}, 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{KleinpeterModarresiAlamInaloo2012, author = {Kleinpeter, Erich and Modarresi-Alam, Ali Reza and Inaloo, Iman Dindarloo}, title = {Synthesis of primary thiocarbamates by silica sulfuric acid as effective reagent under solid-state and solution conditions}, issn = {0022-2860}, year = {2012}, abstract = {A simple and efficient method for the conversion of alcohols and phenols to primary O-thiocarbamates and S- thiocarbamates in the absence of solvent (solvent-free condition) using silica sulfuric acid (SiO2OSO3H) as a solid acid is described. The products are easily distinguished by IR, NMR and X-ray data. X-ray data of the compounds reveal a planar trigonal orientation of the NH2 nitrogen atom with the partial C,N double-bond character and the CS or CO groups in synperiplanar position with CarylO and CalkylS moieties, respectively. Moreover, the OCSNH2 group which is perpendicular to the plane of the benzene ring in 1c and the central thiocarbamate SCONH2 group in 2b are essentially planar.}, language = {en} } @article{KleinpeterCsuetoertoekiSzatmarietal.2012, author = {Kleinpeter, Erich and Cs{\"u}t{\"o}rt{\"o}ki, Ren{\´a}ta and Szatm{\´a}ri, Istv{\´a}n and Heydenreich, Matthias and Koch, Andreas and Starke, Ines and Fulop, Ferenc}, title = {Novel piperidine-fused benzoxazino- and quinazolinonaphthoxazines-synthesis and conformational study}, issn = {0040-4020}, year = {2012}, abstract = {The reactions of 1-(amino(2-hydroxyphenyl)methyl)-2-naphthol (3) and 1-(amino(2-aminophenyl)methyl)-2-naphthol (6) with glutardialdehyde resulted in the formation of piperidine-fused benzoxazinonaphthoxazine 4 and quinazolinonaphthoxazine 7, respectively, both in diastereopure form. The full conformational search protocols of 4 and 7 were successfully carried out by NMR spectroscopy and accompanying molecular modelling; the global minimum-energy conformers of all diastereomers were computed, and the assignments of the most stable stereoisomers, Gtct1 for 4 and Gtct1 for 7, were corroborated by spatial NOE information relating to the H7a-H10a-H15b and H,H coupling patterns of the protons in the flexible part of the piperidine moiety. Additionally, mass spectrometric fragmentation was investigated in collision-induced dissociation experiments. The elemental compositions of the ions were determined by accurate mass measurements.}, language = {en} } @article{KleinpeterSchainyanKirpichenko2012, author = {Kleinpeter, Erich and Schainyan, Bagrat A. and Kirpichenko, Svetlane V.}, title = {Synthesis and conformational properties of 1,3-dimethyl-3-phenyl-1,3-azasilinane : low temperature dynamic NMR and computational study}, issn = {1551-7004}, year = {2012}, abstract = {1,3-Dimethyl-3-phenyl-1,3-azasilinane was synthesized and its conformational behavior was studied by the low temperature NMR spectroscopy and quantum chemical calculations. The compound was shown to exist as an equilibrium mixture of the PhaxMeeq and PheqMeax chair conformers with the N-methyl substituent in equatorial position. The barrier to ring inversion was also determined.}, 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{KleinpeterBranacStojanoviKoch2012, author = {Kleinpeter, Erich and Branac-Stojanovi, Marija and Koch, Andreas}, title = {Is the Conventional Interpretation of the Anisotropic Effects of CC Double Bonds and Aromatic Rings in NMR Spectra in Terms of the -Electron Shielding/Deshielding Contributions Correct?}, issn = {1521-3765}, year = {2012}, abstract = {Based on the nucleus-independent chemical shift (NICS) concept, isotropic magnetic shielding values have been computed along the three Cartesian axes for ethene, cyclobutadiene, benzene, naphthalene, and benzocyclobutadiene, starting from the molecular/ring center up to 10;{\AA} away. These through-space NMR spectroscopic shielding (TSNMRS) values, which reflect the anisotropic effects, have been broken down into contributions from localized- and canonical molecular orbitals (LMOs and CMOs); these contributions revealed that the proton NMR spectroscopic chemical shifts of nuclei that are spatially close to the C=C double bond or the aromatic ring should not be explained in terms of the conventionally accepted ;-electron shielding/deshielding effects. In fact, these effects followed the predictions only for the antiaromatic cyclobutadiene ring.}, language = {en} } @article{KleinpeterLazarevaShainyanetal.2012, author = {Kleinpeter, Erich and Lazareva, Nataliya F. and Shainyan, Bagrat A. and Schilde, Uwe and Chipania, Nina N.}, title = {Synthesis, Molecular Structure, Conformational Analysis, and Chemical Properties of Silicon-Containing Derivatives of Quinolizidine}, issn = {0022-3263}, year = {2012}, 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{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{KleinpeterNeuvonenNeuvonenetal.2011, author = {Kleinpeter, Erich and Neuvonen, Kari and Neuvonen, Helmi and Koch, Andreas}, title = {NBO analysis of polar and steric effect using the axial-equatorial equilibrium of cyclohexyl acetates as a probe}, issn = {2210-271X}, year = {2011}, language = {en} } @article{KleinpeterStojanovicMarkovicetal.2012, author = {Kleinpeter, Erich and Stojanovic, Milovan and Markovic, Rade and Baranac-Stojanovic, Marija}, title = {Synthesis of thiazolidine-fused heterocycles via exo-mode cyclizations of vinylogous N-acyliminium ions}, issn = {1477-0520}, year = {2012}, abstract = {Syntheses of thiazolidine-fused heterocycles via exo-mode cyclizations of vinylogous N-acyliminium ions incorporating heteroatom-based nucleophiles have been examined and discussed. The formation of (5,6)-membered systems was feasible with all nucleophiles tried (O, S and N), while the closing of the five-membered ring was restricted to O- and S-nucleophiles. The closure of a four-membered ring failed. Instead, the bicyclic (5,6)-membered acetal derivative and the tricyclic system with an eight-membered central ring were obtained from the substrates containing O and S nucleophilic moieties, respectively. The reaction outcome and stereochemistry are rationalized using quantum chemical calculations at B3LYP/6-31G(d) level. The exclusive cis-stereoselectivity in the formation of (5,6)- and (5,5)-membered systems results from thermodynamic control, whereas the formation of the eight-membered ring was kinetically controlled.}, language = {en} } @article{KleinpeterNeuvonenNeuvonenetal.2012, author = {Kleinpeter, Erich and Neuvonen, Kari and Neuvonen, Helmi and Koch, Andreas}, title = {Taft equation in the light of NBO computations : Introduction of a novel polar computational substituent constant scale for alkyl groups}, issn = {2210-271X}, year = {2012}, 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} }