TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Antiaromaticity proved by the anisotropic effect in H-1 NMR Spectra JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory N2 - 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). Y1 - 2012 U6 - https://doi.org/10.1021/jp300860q SN - 1089-5639 VL - 116 IS - 23 SP - 5674 EP - 5680 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Csütörtöki, Renata A1 - Szatmari, Istvan A1 - Koch, Andreas A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich A1 - Fulop, Ferenc T1 - Syntheses and conformational analyses of new naphth[1,2-e][1,3]oxazino[3,2-c] quinazolin-13-ones JF - Tetrahedron N2 - 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 A(1), but also the rearranged chain form A(2) as a new tautomer were detected in DMSO at room temperature. The quantity of A(2) 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. KW - Naphthoxazinoquinazolinones KW - Aminonaphthols KW - NMR spectroscopy KW - Conformational analysis KW - Theoretical calculations KW - Ring current effect Y1 - 2012 U6 - https://doi.org/10.1016/j.tet.2012.04.026 SN - 0040-4020 VL - 68 IS - 24 SP - 4600 EP - 4608 PB - Elsevier CY - Oxford ER - TY - CHAP A1 - Machumi, F. A1 - Yenesew, Abiy A1 - Midiwo, J. O. A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich A1 - Khan, S. A1 - Tekwani, B. L. A1 - Walker, L. A. A1 - Muhammad, I T1 - Antiparasitic and anticancer carvotacetone derivatives from Sphaeranthus bullatus T2 - Planta medica : journal of medicinal plant and natural product research Y1 - 2012 SN - 0032-0943 VL - 78 IS - 11 SP - 1201 EP - 1202 PB - Thieme CY - Stuttgart ER - TY - JOUR A1 - Csuetoertoeki, Renata A1 - Szatmari, Istvan A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Starke, Ines A1 - Fueloep, Ferenc A1 - Kleinpeter, Erich T1 - Novel piperidine-fused benzoxazino- and quinazolinonaphthoxazines-synthesis and conformational study JF - TETRAHEDRON N2 - 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 benzox-azinonaphthoxazine 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, G(tct)(1) for 4 and G(tct)(1) for 7, were corroborated by spatial NOE information relating to the H-7a-H-10a-H-15b 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. (C) 2012 Elsevier Ltd. All rights reserved. KW - Quinazolines KW - Naphthoxazines KW - DFT structural study KW - Conformational analysis KW - NMR spectroscopy Y1 - 2012 U6 - https://doi.org/10.1016/j.tet.2012.05.048 SN - 0040-4020 VL - 68 IS - 31 SP - 6284 EP - 6288 PB - PERGAMON-ELSEVIER SCIENCE LTD CY - OXFORD ER - TY - JOUR A1 - Machumi, Francis A1 - Yenesew, Abiy A1 - Midiwo, Jacob O. A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich A1 - Tekwani, Babu L. A1 - Khan, Shabana I. A1 - Walker, Larry A. A1 - Muhammad, Ilias T1 - Antiparasitic and anticancer carvotacetone derivatives of Sphaeranthus bullatus JF - Natural product communications : an international journal for communications and reviews N2 - 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. KW - Sphaeranthus bullatus KW - Asteraceae KW - Antiplasmodial KW - Antileishmanial KW - Anticancer KW - Carvotacetones Y1 - 2012 SN - 1934-578X VL - 7 IS - 9 SP - 1123 EP - 1126 PB - NPC CY - Westerville ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kirpichenko, Svetlana V. A1 - Kleinpeter, Erich T1 - Synthesis and conformational analysis of 1,3-azasilinanes JF - Tetrahedron N2 - 1-Isopropyl-3-methyl-3-phenyl-1,3-azasilinane 1 and 1-isopropyl-3,3-dimethyl-1,3-azasilinane 2 were synthesized and a detailed analysis of their NMR spectra, conformational equilibria and ring inversion processes is presented. Low temperature H-1/C-13 NMR spectroscopy, iteration of the H-1 NMR spectra and quantum chemical calculations showed slight predominance of the PheqMeax over the PhaxMeeq conformer of 1 at low temperature. The barrier for the chair to chair interconversion of both compounds was measured to be 8.25 kcal/mol. KW - 1,3-Azasilinanes KW - Conformational analysis KW - Dynamic NMR spectroscopy KW - Quantum chemical calculations KW - Ring current effect Y1 - 2012 U6 - https://doi.org/10.1016/j.tet.2012.05.106 SN - 0040-4020 VL - 68 IS - 36 SP - 7494 EP - 7501 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Modarresi-Alam, Ali Reza A1 - Inaloo, Iman Dindarloo A1 - Kleinpeter, Erich T1 - Synthesis of primary thiocarbamates by silica sulfuric acid as effective reagent under solid-state and solution conditions JF - Journal of molecular structure N2 - 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 (equivalent to SiO2-OSO3H) 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 C=S or C=O groups in synperiplanar position with C-aryl-O and C-alkyl-S moieties, respectively. Moreover, the -O-CS-NH2 group which is perpendicular to the plane of the benzene ring in 1c and the central thiocarbamate -S-CO-NH2 group in 2b are essentially planar. KW - Solvent-free KW - N-unsubstituted(primary)O-thiocarbamates KW - N-unsubstituted (primary)S-thiocarbamates KW - Isothiocyanic acid KW - Solid acid KW - Silica sulfuric acid Y1 - 2012 U6 - https://doi.org/10.1016/j.molstruc.2012.05.033 SN - 0022-2860 VL - 1024 IS - 9 SP - 156 EP - 162 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kirpichenko, Svetlana V. A1 - Shainyan, Bagrat A. A1 - Kleinpeter, Erich T1 - Unusual conformational preferences of 1,3-dimethyl-3-isopropoxy-3-silapiperidine JF - Journal of physical organic chemistry N2 - The conformational analysis of the first representative of the Si-alkoxy substituted six-membered Si,N-heterocycles, 1,3-dimethyl-3-isopropoxy-3-silapiperidine, was performed by low-temperature 1H and 13C NMR spectroscopy and DFT theoretical calculations. In contrast to the expectations from the conformational energies of methyl and alkoxy substituents, the Meaxi-PrOeq conformer was found to predominate in the conformational equilibrium in the ratio Meaxi-PrOeq : Meeqi-PrOax of ca. 2 : 1 as from the 1H and 13C NMR study. The thermodynamic parameters obtained by the complete line shape analysis showed that the main contribution to the barrier to ring inversion originates from the entropy term of the free energy of activation. KW - barrier to ring inversion KW - conformational equilibrium KW - DFT theoretical calculations KW - dynamic NMR KW - silapiperidines Y1 - 2012 U6 - https://doi.org/10.1002/poc.3028 SN - 0894-3230 VL - 25 IS - 12 SP - 1321 EP - 1327 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Baranac-Stojanovic, Marija A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Density Functional Calculations of the Anisotropic Effects of Borazine and 1,3,2,4-Diazadiboretidine JF - ChemPhysChem : a European journal of chemical physics and physical chemistry N2 - 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. KW - anisotropic effects KW - aromaticity KW - B,N heterocycles KW - density functional calculations KW - NMR spectroscopy Y1 - 2012 U6 - https://doi.org/10.1002/cphc.201200732 SN - 1439-4235 VL - 13 IS - 17 SP - 3803 EP - 3811 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - (Anti)aromaticity of dehydroannulenes of various ring size proved by the ring current effect in H-1 NMR spectra JF - Tetrahedron N2 - 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. KW - Dehydro[n]annulenes KW - (Anti)aromaticity KW - TSNMRS KW - H-1 NMR spectroscopy KW - Anisotropic effect KW - Theoretical calculations KW - ICSS Y1 - 2013 U6 - https://doi.org/10.1016/j.tet.2012.12.019 SN - 0040-4020 VL - 69 IS - 5 SP - 1481 EP - 1488 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Werner, Peter A1 - Koch, Andreas T1 - Push-pull allenes-conjugation, (anti)aromaticity and quantification of the push-pull character JF - Tetrahedron N2 - Structures, H-1/C-13 chemical shifts, and pi electron distribution/conjugation of an experimentally available and theoretically completed set of push-pull allenes Acc(2)C=C=CDon(2) (Acc=F, CHO, CF3, C N; Don=t-Bu, OMe, OEt, SMe, SEt, NCH2R) have been computed at the OFT level of theory. Both orthogonal linear and orthogonal bent structures have been obtained. In the latter case the push-pull character could be quantified by the quotient method. The C-13 chemical shift of the central allene carbon atom C-2 and chemical shift differences Delta delta(C-1, C-2) and Delta delta(C-2, C-3) of allene carbon atoms proved to be a quantitative alternative. TSNMRS of ring-closed push-pull allenes have been computed in addition and were employed to identify polar, carbene-like and carbone-like canonical structures of these molecules. KW - Push-pull allenes KW - Push-pull character KW - C-13 NMR spectroscopy KW - Quotient method KW - TSNMRS KW - ICSS KW - Aromaticity Y1 - 2013 U6 - https://doi.org/10.1016/j.tet.2013.01.027 SN - 0040-4020 VL - 69 IS - 11 SP - 2436 EP - 2445 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kirpichenko, Svetlana V. A1 - Kleinpeter, Erich A1 - Shlykov, Sergey A. A1 - Osadchiy, Dmitriy Yu A1 - Chipanina, Nina N. A1 - Oznobikhina, Larisa P. T1 - 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 JF - The journal of organic chemistry N2 - 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. Y1 - 2013 U6 - https://doi.org/10.1021/jo400289g SN - 0022-3263 VL - 78 IS - 8 SP - 3939 EP - 3947 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Nitschke, Felix A1 - Wang, Peixiang A1 - Schmieder, Peter A1 - Girard, Jean-Marie A1 - Awrey, Donald E. A1 - Wang, Tony A1 - Israelian, Johan A1 - Zhao, XiaoChu A1 - Turnbull, Julie A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich A1 - Steup, Martin A1 - Minassian, Berge A. T1 - Hyperphosphorylation of glucosyl C6 carbons and altered structure of glycogen in the neurodegenerative epilepsy lafora disease JF - Cell metabolism N2 - Laforin or malin deficiency causes Lafora disease, characterized by altered glycogen metabolism and teenage-onset neurodegeneration with intractable and invariably fatal epilepsy. Plant starches possess small amounts of metabolically essential monophosphate esters. Glycogen contains similar phosphate amounts, which are thought to originate from a glycogen synthase error side reaction and therefore lack any specific function. Glycogen is also believed to lack monophosphates at glucosyl carbon C6, an essential phosphorylation site in plant starch metabolism. We now show that glycogen phosphorylation is not due to a glycogen synthase side reaction, that C6 is a major glycogen phosphorylation site, and that C6 monophosphates predominate near centers of glycogen molecules and positively correlate with glycogen chain lengths. Laforin or malin deficiency causes C6 hyperphosphorylation, which results in malformed long-chained glycogen that accumulates in many tissues, causing neurodegeneration in brain. Our work advances the understanding of Lafora disease pathogenesis and suggests that glycogen phosphorylation has important metabolic function. Y1 - 2013 U6 - https://doi.org/10.1016/j.cmet.2013.04.006 SN - 1550-4131 SN - 1932-7420 VL - 17 IS - 5 SP - 756 EP - 767 PB - Cell Press CY - Cambridge ER - TY - JOUR A1 - Neuvonen, Kari A1 - Neuvonen, Helmi A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Nature of the steric Omega(S), E-R and E-S ' substituent constants - comparison with the aid of NBO and STERIC analysis JF - Computational and theoretical chemistry N2 - The nature of the major steric substituent constant scales for alkyl substituents, i.e. Omega(S), E-R and E-S' scales, was studied with the aid of the NBO and the natural steric (STERIC) analyses. Cyclohexyl esters R-3-CCOOC6H11 (R = alkyl or H) were used as the model compounds. Special emphasis was laid on the potential contribution of the polar component in these steric substituent parameters. In the light of our model the Omega(S) scale seems to be dominantly a steric substituent constant scale as is seen on the strengths of the good correlation between the Omega(S) constants of the CR3 group and the total steric exchange energy values E-TSEE for the model compounds. However, the Omega(S) values also seem to include a minor electronic component due to the varying electrostatic effect via the C alpha atom. On the other hand, E-R and E-S' parameters largely hinge on the size dependent polar effect of the CR3 alkyl group. By way of our model this repulsive interaction can be quantified by descriptor Delta q(OCO), the natural charge difference q(C)(C=O) - Sigma qO for the O-C(=O) functional group. Delta q(OCO) depends on the E-TSEE values, on qC alpha and on the polarization coefficients of the oxygen hybrid in the NBO of the pi(C=O) bond. The size sensitivity of the kinetic E-S' constants can be connected to variation of the Burgi-Dunitz angle in the transition state for the standard reaction used. A comparison is made for the q(C)(C=O) or Delta q(OCO) values computed on the one hand with the NBO formalism and on the other hand with the Hirshfeld formalism. A practical novel substituent constant q(C)(C=O) for the size of the alkyl groups is introduced. KW - NBO and STERIC analyses KW - Taft equation KW - Steric substituent constant KW - Steric effect KW - Polar effect Y1 - 2013 U6 - https://doi.org/10.1016/j.comptc.2013.03.025 SN - 2210-271X VL - 1015 IS - 4 SP - 34 EP - 43 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kleinpeter, Erich T1 - Silacyclohexanes and silaheterocyclohexanes-why are they so different from other heterocyclohexanes? JF - Tetrahedron N2 - Stereochemical studies on silaheterocyclohexanes is a 'hot topic' as evidenced by the growing number of publications. During last 10 years a substantial number of substituted silacyclohexanes and heterocyclohexanes containing sulfur, oxygen or nitrogen as the second (or third) heteroatom have been synthesized and studied by variable temperature dynamic NMR spectroscopy, gas-phase electron diffraction, variable temperature IR, Raman, microwave spectroscopy with respect to thermodynamic (frozen conformational equilibria) and kinetic (barrier to ring inversion) information. As the stereochemistry of cyclohexane and its N-, O-, P-, S-hetero analogues is one of keystones of modern theoretical and synthetic organic and heterocyclic chemistry, the stereochemistry of silacyclohexane and its hetero analogs is an important element of theoretical and synthetic organosilicon chemistry. The various classes of saturated six-membered rings were critically compared and studied in detail with respect to differences in their stereochemistry and dynamic behavior. KW - Silacyclohexanes KW - Silaheterocyclohexanes KW - Conformational equilibrium KW - Barrier to ring inversion KW - Steric effects KW - Electrostatic effects Y1 - 2013 U6 - https://doi.org/10.1016/j.tet.2013.04.126 SN - 0040-4020 VL - 69 IS - 29 SP - 5927 EP - 5936 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Dzambaski, Zdravko A1 - Markovic, Rade A1 - Kleinpeter, Erich A1 - Baranac-Stojanovic, Marija T1 - 2-Alkylidene-4-oxothiazolidine S-oxides - synthesis and stereochemistry JF - Tetrahedron N2 - 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. KW - 2-Alkylidene-4-oxothiazolidine KW - Sulfoxide KW - Diastereoselectivity KW - Density functional calculations KW - CH center dot center dot center dot O hydrogen bonds Y1 - 2013 U6 - https://doi.org/10.1016/j.tet.2013.05.087 SN - 0040-4020 VL - 69 IS - 31 SP - 6436 EP - 6447 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Szatmari, Istvan A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Fulop, Ferenc A1 - Kleinpeter, Erich T1 - Unexpected isomerization of new naphth[1,3]oxazino[2,3-a] isoquinolines in solution, studied by dynamic NMR and supported by theoretical DFT computations JF - Tetrahedron N2 - Through the reactions of 1-aminomethyl-2-naphthol and substituted 1-aminobenzyl-2-naphthols with 3,4-dihydroisoquinoline or 6,7-dimethoxy-3,4-dihydroisoquinoline under microwave conditions, naphth[1,2-e][1,3]oxazino[2,3-a]-isoquinoline derivatives were prepared in good yields. The latter reaction was extended by using 2-aminoarylmethyl-1-naphthols, leading to isomeric naphth-[2,1-e][1,3]oxazino[2,3-a] isoquinolines. Beside the detailed NMR spectroscopic and theoretical study of both stereochemistry and dynamic behaviour of these new conformational flexible heterocyclic ring systems an unexpected dynamic process between two diastereomers was observed in solution, studied by variable temperature H-1 NMR spectroscopy and the mechanism proved by theoretical DFT computations. KW - 3,4-Dihydroisoquinoline KW - Aminonaphthol KW - Dynamic NMR spectroscopy KW - DFT calculations KW - Conformational analysis Y1 - 2013 U6 - https://doi.org/10.1016/j.tet.2013.06.094 SN - 0040-4020 VL - 69 IS - 35 SP - 7455 EP - 7465 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Rasovic, Aleksandar A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Markovic, Rade T1 - Studies of the regioselective ring-opening closing mode of functionally different thiazolidine type enaminones - en route to the synthesis of trithiaazapentalene derivatives JF - Tetrahedron N2 - Trithiaazapentalene derivatives were prepared by the reaction of 2-alkylidene-4-oxothiazolidines with Lawesson's reagent. They are classified as two structurally different trithiaazapentalene compounds that have different contributions of monocyclic 1,2-dithiole and 1,2,4-dithiazole structures and degrees of aromaticity of the bicyclic trithiaazapentalene system. The electron-donating ability of substituents at the C(5) position of the trithiaazapentalene system is recognized as the main cause for changes in pi-Celectron distribution. This is the first complete study of substituent effects on the structure of trithiapentalenes. (C) 2013 Elsevier Ltd. All rights reserved. KW - Trithiapentalene KW - 1,2-Dithiole KW - 1,2,4-Dithiazole KW - 4-Oxothiazolidine KW - Rearrangement to trithiaazapentalene KW - Push-pull character Y1 - 2013 U6 - https://doi.org/10.1016/j.tet.2013.10.088 SN - 0040-4020 VL - 69 IS - 51 SP - 10849 EP - 10857 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Lazareva, Nataliya F. A1 - Albanov, Alexander I. A1 - Shainyan, Bagrat A. A1 - Kleinpeter, Erich T1 - Synthesis and conformational properties of substituted 1,4,2-oxazasilinanes: low temperature NMR study and quantum chemical calculations Y1 - 2012 UR - http://www.sciencedirect.com/science/article/pii/S0040402011018321 U6 - https://doi.org/10.1016/j.tet.2011.11.077 ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Suslova, Elena N. A1 - Kleinpeter, Erich T1 - Conformational analysis of 4,4-dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane and 2,2,6,6-tetramethyl-4- (trifluoromethylsulfonyl)-1,4,2,6-oxazadisilinane N2 - 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. Y1 - 2012 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Lämmermann, Anica A1 - Kühn, Heiner T1 - The anisotropic effect of functional groups in H-1 NMR spectra is the molecular response property of spatial nucleus independent chemical shifts (NICS)-Conformational equilibria of exo/endo tetrahydrodicyclopentadiene derivatives N2 - The inversion of the flexible five-membered ring in tetrahydrodicyclopentadiene (TH-DCPD) derivatives remains fast on the NMR timescale even at 103 K. Since the intramolecular exchange process could not be sufficiently slowed for spectroscopic evaluation, the conformational equilibrium is thus inaccessible by dynamic NMR. Fortunately, the spatial magnetic properties of the aryl and carbonyl groups attached to the DCPD skeleton can be employed in order to evaluate the conformational state of the system. In this context, the anisotropic effects of the functional groups in the H-1 NMR spectra prove to be the molecular response property of spatial nucleus independent chemical shifts (NICS). Y1 - 2011 ER - TY - JOUR A1 - Kramer, Markus A1 - Kleinpeter, Erich T1 - A conformational study of N-acetyl glucosamine derivatives utilizing residual dipolar couplings Y1 - 2013 SN - 1090-7807 ER - TY - JOUR A1 - Stojanovic, Milovan A1 - Markovic, Rade A1 - Kleinpeter, Erich A1 - Baranac-Stojanovic, Marija T1 - endo-Mode cyclizations of vinylogous N-acyliminium ions as a route to the synthesis of condensed thiazolidines Y1 - 2011 SN - 0040-4020 ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kleinpeter, Erich T1 - Conformational preferences of Si-Ph,H and Si-Ph,Me silacyclohexanes and 1,3-thiasilacyclohexanes : Additivity of conformational energies in 1,1-disubstituted heterocyclohexanes N2 - 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. Y1 - 2012 UR - http://www.sciencedirect.com/science/article/pii/S0040402011016620 (25.11.2013) SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Spatial magnetic properties subject to lone pair and pi electron delocalization in benzenoid and quinoid structures : are quinoid tautomers really nonaromatic? N2 - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzenoid and quinoid tautomeric structures such as benzodifurantrione and phenazine-type molecules have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept of Paul von Rague Schleyer and visualized as iso- chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the partial aromaticity of the studied compounds. In the case of the surprisingly more stable quinoid tautomers, the aromaticity-synonymous with stability due to the conjugation of p electrons and lone pairs-was not found to be particularly reduced. Y1 - 2012 SN - 1551-7004 ER - TY - JOUR A1 - Csütörtöki, Renáta A1 - Szatmári, István A1 - Koch, Andreas A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich A1 - Fulop, Ferenc T1 - Synthesis and conformational analysis of new naphth[1,2-e][1,3]oxazino[3,4-c]quinazoline derivatives Y1 - 2011 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Chelatoaromaticity-existing: yes or no? An answer given by spatial magnetic properties (through space NMR shieldings-TSNMRS) Y1 - 2011 SN - 1463-9076 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - 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 N2 - 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. Y1 - 2011 UR - http://www.sciencedirect.com/science/article/pii/S0040402011008507 (13.9.13) SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Kirpichenko, Svetlana V. A1 - Ushakov, Igor A. A1 - Shainyan, Bagrat A. T1 - Conformational analysis of 3-methyl-3-silathiane and 3-fluoro-3-methyl-3-silathiane N2 - 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. Y1 - 2011 SN - 0894-3230 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Linker, Torsten T1 - Synthesis and NMR spectroscopic conformational analysis of esters of 4-hydroxy-cyclohexanone-the more polar the molecule the more stable the axial conformer N2 - 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. Y1 - 2012 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Shainyan, Bagrat A. A1 - Kirpichenko, Svetlana V. A1 - Shlykov, Sergei A. T1 - Structure and Conformational Properties of 1,3,3-Trimethyl-1,3-Azasilinane : Gas Electron Diffraction, Dynamic NMR, and Theoretical Study. Y1 - 2012 SN - 1089-5639 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Csütörtöki, Renáta A1 - Szatmári, István A1 - Koch, Andreas A1 - Fulop, Ferenc T1 - Syntheses and conformational analyses of new naphth[1,2-e][1,3]oxazino[3,2-c]quinazolin-13-ones N2 - 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. Y1 - 2012 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Lammermann, Anica A1 - Kühn, Heiner T1 - Synthesis and NMR spectra of the syn and anti isomers of substituted cyclobutanes-evidence for steric and spatial hyperconjugative interactions N2 - 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. Y1 - 2011 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich T1 - 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) N2 - 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. Y1 - 2012 SN - 1463-9076 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Modarresi-Alam, Ali Reza A1 - Inaloo, Iman Dindarloo T1 - Synthesis of primary thiocarbamates by silica sulfuric acid as effective reagent under solid-state and solution conditions N2 - 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. Y1 - 2012 SN - 0022-2860 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Csütörtöki, Renáta A1 - Szatmári, István A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Starke, Ines A1 - Fulop, Ferenc T1 - Novel piperidine-fused benzoxazino- and quinazolinonaphthoxazines-synthesis and conformational study N2 - 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. Y1 - 2012 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Schainyan, Bagrat A. A1 - Kirpichenko, Svetlane V. T1 - Synthesis and conformational properties of 1,3-dimethyl-3-phenyl-1,3-azasilinane : low temperature dynamic NMR and computational study N2 - 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. Y1 - 2012 SN - 1551-7004 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Balci, Kubilay A1 - Yapar, G. A1 - Akkaya, S. A1 - Akyuz, S. A1 - Koch, Andreas T1 - A conformational analysis and vibrational spectroscopic investigation on 1,2-bis(o-carboxyphenoxy) ethane molecule N2 - 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. Y1 - 2012 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Branac-Stojanovi, Marija A1 - Koch, Andreas T1 - 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? N2 - 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;Å 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. Y1 - 2012 SN - 1521-3765 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Lazareva, Nataliya F. A1 - Shainyan, Bagrat A. A1 - Schilde, Uwe A1 - Chipania, Nina N. T1 - Synthesis, Molecular Structure, Conformational Analysis, and Chemical Properties of Silicon-Containing Derivatives of Quinolizidine Y1 - 2012 SN - 0022-3263 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Shainyan, Bagrat A. A1 - Suslova, Elena N. T1 - Conformational analysis of N-phenyl- and N-trifyl-4,4-dimethyl-4-silathiane 1-sulfimides Y1 - 2011 SN - 0894-3230 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Shainyan, Bagrat A. A1 - Suslova, Elena N. T1 - Conformational analysis of 4,4-dimethyl-4-silathiane and its S-oxides Y1 - 2011 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Neuvonen, Kari A1 - Neuvonen, Helmi A1 - Koch, Andreas T1 - NBO analysis of polar and steric effect using the axial-equatorial equilibrium of cyclohexyl acetates as a probe Y1 - 2011 SN - 2210-271X ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Stojanovic, Milovan A1 - Markovic, Rade A1 - Baranac-Stojanovic, Marija T1 - Synthesis of thiazolidine-fused heterocycles via exo-mode cyclizations of vinylogous N-acyliminium ions N2 - 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. Y1 - 2012 SN - 1477-0520 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Neuvonen, Kari A1 - Neuvonen, Helmi A1 - Koch, Andreas T1 - Taft equation in the light of NBO computations : Introduction of a novel polar computational substituent constant scale for alkyl groups Y1 - 2012 SN - 2210-271X ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Pihlaja, Kalevi A1 - Sinkkonen, Jari A1 - Stájer, Gezá A1 - Koch, Andreas T1 - 1-Oxo-1,3-dithiolanesùsynthesis and stereochemistry N2 - 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. Y1 - 2011 SN - 0749-1581 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Marsat, Jean-Noël A1 - Heydenreich, Matthias A1 - von Berlepsch, Hans A1 - Laschewsky, André T1 - Self-Assembly into Multicompartment Micelles and Selective Solubilization by Hydrophilic-Lipophilic- Fluorophilic Block Copolymers Y1 - 2011 SN - 0024-9297 ER - TY - JOUR A1 - Wacker, Philipp A1 - Dahms, Katja A1 - Senge, Mathias O. A1 - Kleinpeter, Erich T1 - Conformational Landscape of meso-(1,3-Dithian-2-yl)porphyrins N2 - 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. Y1 - 2007 UR - http://pubs.acs.org/doi/full/10.1021/jo0708700 U6 - https://doi.org/10.1021/Jo0708700 ER - TY - BOOK A1 - Kleinpeter, Erich A1 - Klod, Sabrina A1 - Koch, Andreas T1 - Endohedral and external through-space shieldings of the fullerenes C50, C60, C60-6, C70, and C70-6- visualization of (Anti)aromaticity and their effects on the chemical shifts of encapsulated nuclei N2 - Endohedral and external through-space NMR shieldings (TSNMRS) and the magnetic susceptibilities of the fullerene carbon cages of C50, C60, C60-6, C70, and C70-6 were assessed by ab initio molecular orbital calculations. Employing the nucleus-independent chemical shift (NICS) concept, these TSNMRS were visualized as isochemical shielding surfaces (ICSS) and were applied to quantitatively estimate either the aromaticity or the anti-aromaticity on the fullerene surface pertaining to the five- or six-membered ring moieties and the shielding of any nuclei enclosed within the carbon cages. Differences between the NICSs calculated at the center of the fullerene carbon cages and the experimental chemical shifts of encapsulated NMR-active nuclei as well as experimental shieldings observed for different encapsulated nuclei were able to be understood readily for the first time. Y1 - 2008 UR - http://pubs.acs.org/doi/full/10.1021/jo702316h U6 - https://doi.org/10.1021/jo702316h ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas A1 - Seidl, Peter R. T1 - Visualization and quantification of the anisotropic effect of C=C double bonds on 1H NMR spectra of highly congested hydrocarbons-indirect estimates of steric strain N2 - The anisotropic effect of the olefinic C=C double bond has been calculated by employing the NICS (nucleus independent chemical shift) concept and visualized as an anisotropic cone by a through space NMR shielding grid. Sign and size of this spatial effect on 1H chemical shifts of protons in norbornene, exo- and endo-2-methylnorbornenes, and in three highly congested tetracyclic norbornene analogs have been compared with the experimental 1H NMR spectra as far as published. 1H NMR spectra have also been calculated at the HF/6-31G* level of theory to get a full, comparable set of proton chemical shifts. Differences between ;(1H)/ppm and the calculated anisotropic effect of the C=C double bond are discussed in terms of the steric compression that occurs in the compounds studied. Y1 - 2008 UR - http://pubs.acs.org/doi/full/10.1021/jp801063t U6 - https://doi.org/10.1021/Jp801063t ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas A1 - Sahoo, Himansu S. A1 - Chand, Dillip Kumar T1 - Anisotropic effect of the nitrate anion-manifestation of diamagnetic proton chemical shifts in the 1H NMR spectra of NO3-coordinated complexes N2 - The anisotropic effect of the planar nitrate anion NO3- has been ab initio calculated employing the Nucleus- Independent Chemical Shift (NICS) concept of von Ragué 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. Y1 - 2008 UR - http://www.sciencedirect.com/science/article/pii/S0040402008005814 U6 - https://doi.org/10.1016/j.tet.2008.03.063 ER - TY - JOUR A1 - Koetz, Joachim A1 - Jagielski, Nicole A1 - Kosmella, Sabine A1 - Friedrich, Alwin A1 - Kleinpeter, Erich T1 - CdS nanocubes formed in phosphatidylcholin-based template phases N2 - 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 "classicalö 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. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/09277757 U6 - https://doi.org/10.1016/j.colsurfa.2006.01.013 SN - 0927-7757 VL - 288 SP - 43 EP - 1-3 ER - TY - JOUR A1 - Starke, Ines A1 - Kammer, Stefan A1 - Holdt, Hans-Jürgen A1 - Kleinpeter, Erich T1 - Stability of disubstituted copper complexes in the gas phase analyzed by electrospray ionization mass spectrometry N2 - A series of nitrogen ligand (L)/copper complexes of the type [(CuL)-L-I](+), [(CuL)-L-II(X)](+) and [(CuL2)-L- I](+) (X = Cl-, BF4-, acac(-), CH3COO- and SO3CF3-) was studied in the gas phase by electrospray ionization mass spectrometry. The following ligands (L) were employed: 1,12-diazaperylene (dap), 1,1'-bisiso-quinoline (bis), 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen), 2,11-disubstituted 1,12-diazaperylenes (dap), 3,3'- disubstituted 1,1'-bisisoquinoline (bis), 5,8-dimethoxy-substituted diazaperylene (meodap), 6,6'-dimethoxy- substituted bisisoquinoline (meobis) and 2,9-dimethyl-1,10-phenanthroline (dmphen). Collision-induced decomposition measurements were applied to evaluate the relative stabilities of the different copper complexes. The influence of the spatial arrangement of the ligands, of the type of substituents and of the counter ion of the copper salts employed for the complexation was examined. Correlations were found between the binding constants of the [ML2](+) complexes in solution and the relative stabilities of the analogous complexes in the gas phase. Furthermore, complexation with the ligands 2,11-dialkylated 1,12-diazaperylenes [alkyl = ethyl (dedap) and isopropyl (dipdap)] was studied in the solvents CH3OH and CH3CN. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/4849 U6 - https://doi.org/10.1002/Rcm.4519 SN - 0951-4198 ER - TY - JOUR A1 - Fettke, Anja A1 - Kramer, Markus A1 - Kleinpeter, Erich T1 - Lectin-bound conformations and non-covalent interactions of glycomimetic analogs of thiochitobiose N2 - The bound conformations of five S-glycoside analogs of N,N'-diacetylchitobiose as well as their non- covalent interactions with two lectins, Phytolacca americana lectin (PAL) and wheat germ agglutinin (WGA), are reported. The conformations of the ligands were examined by trNOESY experiments and compared with the free, solution-state conformations and molecular modeling data obtained by force field calculations. In the case of S-aryl, S-glycosides with exclusively S-glycosidic linkages, similar free and lectin-bound conformations and non-covalent interactions were found, whereas they differed for mixed glycosides and for a thiazoline derivative. In addition, STD (saturation transfer difference) NMR magnetization transfer efficiencies at three different temperatures were determined and assessed with respect to the structural differences of these pseudosaccharides. The binding epitopes of each substrate with PAL and WGA were also determined. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/00404020 U6 - https://doi.org/10.1016/j.tet.2010.04.012 SN - 0040-4020 ER - TY - JOUR A1 - de Araujo, Martha T. A1 - Chacon, Eluzir P. A1 - Carneiro, José W. de M. A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Analysis of anisotropic effects in trinuclear metal carbonyl compounds by visualization of through-space NMR shielding N2 - 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. Y1 - 2010 UR - http://www.springerlink.com/content/100529 U6 - https://doi.org/10.1007/s00894-010-0662-3 SN - 1610-2940 ER - TY - JOUR A1 - Baranac-Stojanovic, Marija A1 - Klaumuenzer, Ute A1 - Markovic, Rade A1 - Kleinpeter, Erich T1 - Structure, configuration, conformation and quantification of the push pull-effect of 2-alkylidene-4- thiazolidinones and 2-alkylidene-4,5-fused bicyclic thiazolidine derivatives N2 - Structures of a series of push-pull 2-alkylidene-4-thiazolidinones and 2-alkylidene-4,5-fused bicyclic thiazolidine derivatives were optimized at the B3LYP/6-31G(d) level of theory in the gas phase and discussed with respect to configurational and conformational stability. Employing the GIAO method, C-13 NMR chemical shifts of the C-2, C-2', C-4 and C-5 atoms were calculated at the same level of theory in the gas phase and with inclusion of solvent, and compared with experimental data. Push-pull effect of all compounds was quantified by means of the quotient pi*/pi, length of the partial double bond, C-13 NMR chemical shift difference (Delta delta(C=C)) and H-1 NMR chemical shifts of olefinic protons. The effect of bromine on donating and accepting ability of other substituents of the push- pull C=C double bond is discussed, too. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/00404020 U6 - https://doi.org/10.1016/j.tet.2010.09.040 SN - 0040-4020 ER - TY - JOUR A1 - Modarresi-Alam, Ali Reza A1 - Amirazizi, Homeyra Alsadat A1 - Bagheri, Hajar A1 - Bijanzadeh, Hamid-Reza A1 - Kleinpeter, Erich T1 - Dynamic H-1 NMR spectroscopic study of the ring inversion in N-sulfonyl morpholines : studies on N-S interactions N2 - 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. Y1 - 2009 UR - http://pubs.acs.org/journal/joceah U6 - https://doi.org/10.1021/Jo900454a SN - 0022-3263 ER - TY - JOUR A1 - Boehm, Stanislav A1 - Tomašciková, Jana A1 - Imrich, Ján A1 - Danihel, Ivan A1 - Kristian, Pavol A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Klika, Karel D. T1 - 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 N2 - 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. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/01661280 U6 - https://doi.org/10.1016/j.theochem.2009.09.019 SN - 0166-1280 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Holzberger, Anja T1 - Structure, intramolecular flexibility, and complexation of aza crown ethers to anions H2PO4- and HSO4- in nonprotic solvents JF - Tetrahedron N2 - Both the structure and intramolecular flexibility of a series of aza crown ethers were studied by experimental NMR and theoretical molecular modeling. The stoichiometries of complexation to the anions H2PO4- and resulting complex stabilities were determined by experimental NMR (1H, 31P) titration and, in addition, the structure and mobility changes of the aza crown ethers upon complexation were also examined. Y1 - 2006 UR - https://www.sciencedirect.com/science/article/abs/pii/S0040402006012130 U6 - https://doi.org/10.1016/j.tet.2006.07.074 SN - 0040-4020 VL - 62 IS - 43 SP - 10237 EP - 10247 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Balci, Kubilay A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - A comparative vibrational spectroscopic investigation of free mn-12S(2)O(2) and fn-12S(2)O(2) dithiacrown ethers based on DFT calculations N2 - 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. Y1 - 2006 UR - http://www.sciencedirect.com/science/journal/00222860 U6 - https://doi.org/10.1016/j.molstruc.2005.10.048 SN - 0022-2860 ER - TY - JOUR A1 - Lazareva, Nataliya F. A1 - Shainyan, Bagrat A. A1 - Kleinpeter, Erich T1 - 4-Alkyl-2,2,6,6-tetramethyl-1,4,2,6-oxaazadisilinanes : synthesis, structure, and conformational analysis N2 - 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. Y1 - 2010 UR - http://www3.interscience.wiley.com/cgi-bin/jhome/4569 U6 - https://doi.org/10.1002/Poc.1605 SN - 0894-3230 ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Ushakov, Igor A. A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Stereodynamics of 1-(methylsulfonyl)-3,5-bis(trifluoromethylsulfonyl)-1,3,5-triazinane: Experimental and theoretical analysis N2 - Dynamic NMR of 1-(methylsulfonyl)-3,5-bis(trifluoromethylsulfonyl)-1,3,5-triazinane reveals the existence of three conformers and two dynamic processes: ring inversion and rotation about the N-S bond, both processes having Delta G(double dagger) = 13.5 kcal/mol. An unprecedented large reverse Perlin effect (J(CHax) > J(CHeq)) was found experimentally and calculated theoretically. Y1 - 2006 UR - http://pubs.acs.org/doi/full/10.1021/jo061112x U6 - https://doi.org/10.1021/Jo061112x ER - TY - JOUR A1 - Kirpichenko, Svetlana V. A1 - Kleinpeter, Erich A1 - Shainyan, Bagrat A. T1 - Conformational analysis of 3,3-dimethyl-3-silathiane, 2,3,3-trimethyl-3-silathiane and 2-trimethylsilyl-3,3- dimethyl-3-silathianeùpreferred conformers, barriers to ring inversion and substituent effec N2 - 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. Y1 - 2010 SN - 0894-3230 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Boelke, Ute A1 - Koch, Andreas T1 - Subtle Trade-off Existing between (Anti)Aromaticity, Push-Pull Interaction, Keto-Enol Tautomerism, and Steric Hindrance When Defining the Electronic Properties of Conjugated Structures Y1 - 2010 SN - 1089-5639 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Boelke, Ute A1 - Kreicberga, Jana T1 - Quantification of the push-pull character of azo dyes and a basis for their evaluation as potential nonlinear optical materials N2 - The push-pull characters of a large series of donor-acceptor substituted azo dyesù71 structures in allùhave been quantified by the NN double bond lengths, dNN, the 15N NMR chemical shift differences, ;;15N, of the two nitrogen atoms and the quotient, ;*/;, of the occupations of the antibonding ;*, and bonding ; orbitals of this partial NN double bond. The excellent correlation of the occupation quotients with the bond lengths strongly infers that both ;*/; and dNN are excellent parameters for quantifying charge alternation in the push-pull chromophore and the molecular hyperpolarizability, ;0, of these compounds. By this approach, selected compounds can be appropriately considered as viable candidates for nonlinear optical (NLO) applications. Y1 - 2010 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Identification of benzenoid and quinonoid structures by through-space NMR shieldings (TSNMRS) Y1 - 2010 SN - 1089-5639 ER - TY - JOUR A1 - Kramer, Markus A1 - Kleinpeter, Erich T1 - STD-DOSY : a new NMR method to analyze multi-component enzyme/substrate systems N2 - A new approach to analyze multi-component Saturation Transfer Difference (STD) NMR spectra by combining the STD and the DOSY experiment is proposed. The resulting pulse sequence was successfully used to simplify an exemplary multi- component protein/substrate system by means of standard DOSY processing methods. Furthermore, the same experiment could be applied to calculate the ratio of saturated substrate molecules and its saturation rate in the case of competitive interactions. This ratio depends on the strength of this interaction between the substrates and the protein, so that this kind of information could be extracted from the results of our experiment. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/10907807 U6 - https://doi.org/10.1016/j.jmr.2009.11.007 SN - 1090-7807 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Probing the exohedral magnetic properties of C20 derivatives by through space NMR shieldings (TSNMRS) N2 - The through space NMR shieldings (TSNMRS) of dodecahedrane C20H20, of the isomeric hydrocarbons C20H12, of the ions C20H122+ and C20H122- of the fluxional fullerene C20 and of its dication C202+ have been ab initio calculated employing the NICS concept on basis of MP2/6-31G* geometries and visualized as iso-chemical-shielding/deshielding surfaces (ICSSs). TSNMRS values were employed to study the exohedral magnetic properties of the compounds studied. Hereby, the curved It-conjugation in the compounds studied could be quantified. Y1 - 2010 UR - http://www.sciencedirect.com/science/journal/01661280 U6 - https://doi.org/10.1016/j.theochem.2009.09.018 SN - 0166-1280 ER - TY - JOUR A1 - Kihampa, Charles A1 - Nkunya, Mayunga H. H. A1 - Joseph, Cosam C. A1 - Magesa, Stephen M. A1 - Hassanali, Ahmed A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich T1 - Antimosquito and antimicrobial clerodanoids and a chlorobenzoid from Tessmannia species N2 - 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. Y1 - 2010 UR - http://www.naturalproduct.us/ SN - 1934-578X ER - TY - JOUR A1 - Kleinpeter, Erich T1 - Syntheses and conformational analyses of mono- and trans-1,4-dialkoxy substituted cyclohexanes : the steric substituent/skeleton interactions N2 - Mono- and trans-1,4-dialkoxy substituted cyclohexanes (alkyl=Me, Et, i-Pr, t-Bu) were prepared using the solvomercuration-demercuration (SM-DM) procedure. The axialaxial and axial,axialequatorial, equatorial conformational equilibria of the products were studied by low temperature 1H and 13C NMR spectroscopy in CD2Cl2. The structures and relative energies of the participating conformers were calculated at both the B3LYP (6-311G*//6-311+G*) and MP2 (6-311+G*//6-311G*) levels of theory. In the case of DFT, good correlations of ;Gocalcd versus ;Goexptl were obtained. Both the structures and the energy differences of the conformers have been discussed with respect to established models of conformational analysis, viz. steric and hyperconjugative interactions. In addition, 1JH,C coupling constants were considered with respect to the hyperconjugation present. Y1 - 2007 UR - http://www.sciencedirect.com/science/journal/00404020 U6 - https://doi.org/10.1016/j.tet.2007.06.094 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Klod, Sabrina A1 - Koch, Andreas T1 - Visualization of through space NMR shieldings of aromatic and anti-aromatic molecules and a simple means to compare and estimate aromaticity N2 - Through space NMR shieldings of aromatic (benzene, mono-substituted and annelated benzenes, ferrocene, [14]- and [18]-annulenes, phenylenes and tetra- to heptahelicene) and anti-aromatic molecules (cyclobutadiene and pentalene) were assessed by ab initio molecular-orbital calculations. Employing the nucleus-independent chemical shifts (NICS) concept, these through space NMR shieldings were visualized as iso-chemical-shielding surfaces (ICSSs) and can be applied quantitatively to determine the stereochemistry of proximal nuclei. In addition, the distances in Å at ICSS values of ±0.1 ppm in-plane and perpendicular-to-center of the aromatic ring system were employed as a simple means to compare and estimate qualitatively the aromaticity of the systems at hand. Y1 - 2007 UR - http://www.sciencedirect.com/science/journal/01661280 U6 - https://doi.org/10.1016/j.theochem.2007.02.049 SN - 0166-1280 ER - TY - JOUR A1 - Lämmermann, Anica A1 - Szatmári, István A1 - Fulop, Ferenc A1 - Kleinpeter, Erich T1 - Inter- or intramolecular N···H-O or N-H···O Hydrogen bonding in 1,3-Amino-alpha/beta-naphthols : an experimental NMR and computational study N2 - The existence of intermolecular or intramolecular N···H;O or N;H···O hydrogen bonding in three series (series 1, substituted 1-aminoalkyl-2-naphthols: R = H, Me, Et, Pr, i-Pr; series 2, substituted 1-;- aminobenzyl-2-naphthols: H, p-OMe, p-F, p-Cl, p-Br, p-NO2, p-Me; series 3, substituted 2-;-aminobenzyl-1-naphthols: R = H, p-Me, p-F, p-Br, p-OMe, m-NO2, m-Br) are studied by NMR spectroscopy and computed at the DFT level of theory [B3LYP/6-311+G(d,p)]. The correct nature of the H-bond was assigned unequivocally both experimentally and computationally by potential energy scans rotating the involved dihedral angles. We investigated the effects of substituents on the strength of the H-bond by evaluating the corresponding hyperconjugative stabilization energy nlonepair ; ;*X;H and Hammett substituent constant plots. By this means, steric and electronic substituent effects could be easily quantified and separated. Y1 - 2009 UR - http://pubs.acs.org/journal/jpcafh U6 - https://doi.org/10.1021/Jp902731n SN - 1089-5639 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Stamboliyska, Bistra A. T1 - Hyperpolarizability of donor-acceptor azines subject to push-pull character and steric hindrance N2 - The push-pull character of two series of donor-acceptor azines has been quantified by C-13, N-15 chemical shift differences of the partial C(1)=N(1) and N(2)=C(2) double bonds in the central linking C(1)=N(1)-N(2)=C(2) unit and by the quotient of the occupations of the bonding pi and anti-bonding pi* orbitals of these bonds. Excellent correlation of the latter push-pull parameter with the corresponding bond lengths d(C=N) strongly recommend both the occupation quotients pi*/pi and the corresponding bond lengths as reasonable sensors for quantifying the push, pull character along the C=N-N=C linking unit, for the donor-acceptor quality of the two series of azines and for the molecular hyperpolarizability beta(0) of these compounds. Within this context, reasonable conclusions concerning the interplay of steric hindrance in the chromophore, push-pull character and hyperpolarizability of the azines and their application as NLO materials will be drawn. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00404020 U6 - https://doi.org/10.1016/j.tet.2009.09.026 SN - 0040-4020 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Visualization of homoaromaticity in cations, neutral molecules and anions by spatial magnetic properties (through space NMR shieldings) - an 1H/13C NMR chemical shift study N2 - Prototypes for homoaromaticity in cations, neutral molecules, and anions are theoretically studied at the MP2 level of theory. For the global minimum structures on the potential energy surface both 1H/13C chemical shifts and spatial magnetic properties as through space NMR shieldings (TSNMRS) were calculated by the GIAO perturbation method. The TSNMRS are visualized as iso-chemical-shielding surfaces (ICSS) of different sign and size. Coincident experimental and computed 1H/13C chemical shifts afforded the possibility to decide from the TSNMRSs at hand on both the existence and the size of homoaromaticity in the molecules studied. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00404020 U6 - https://doi.org/10.1016/j.tet.2009.04.063 SN - 0040-4020 ER - TY - JOUR A1 - Thóth, Diána A1 - Szatmári, István A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Fulop, Ferenc T1 - Synthesis and conformational analysis of naphthylnaphthoxazine derivatives N2 - Four new primary aminonaphthols (4, 5, 9 and 10) were synthesized from 1- or 2-naphthol and 1- or 2- naphthaldehyde via naphthoxazines in modified Mannich condensations. Simple ring-closure reactions of these aminonaphthols with paraformaldehyde, 4-nitrobenzaldehyde, phosgene or 4-chlorophenyl isothiocyanate led to new heterocyclic derivatives. In these transformations, either an sp2 or an sp3 carbon was inserted between the hydroxy and amino groups. The effects of substituents and the naphthyl ring on the conformation were investigated by means of NMR measurements, employing both dipolar and scalar couplings. The structures were confirmed by DFT quantum chemical calculations involving computed coupling constants, intramolecular distances between nuclei and the relative energies of the preferred conformers. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00222860 U6 - https://doi.org/10.1016/j.molstruc.2009.04.015 SN - 0166-1280 ER - TY - JOUR A1 - Balci, Kubilay A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - A theoretical IR spectroscopic study based on DFT calculations for free mn-15S(2)O(3) maleonitrile-dithiacrown ether compound N2 - 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. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00222860 U6 - https://doi.org/10.1016/j.molstruc.2008.08.027 SN - 0022-2860 ER - TY - JOUR A1 - Fettke, Anja A1 - Peikow, Dirk A1 - Peter, Martin G. A1 - Kleinpeter, Erich T1 - Synthesis and conformational analysis of glycomimetic analogs of thiochitobiose N2 - The synthesis of six analogs of N,N;-diacetylchitobiose is reported, including a novel transglycosylation reaction for the preparation of S-aryl thioglycosides. The conformations of the compounds were studied by a combination of NMR spectroscopy and molecular modeling, using force field calculations. In the case of the S-aryl thioglycosides with exclusively S-glycosidic linkages, dihedral angles of the disaccharidic S-glycosidic bonds, ;; and ;; and of the S-arylglycoside bonds, ; and ;, were found to be similar, whereas they were different in mixed glycosides and in a thiazoline derivative. An adequate correlation between the calculated H,H-distances of the local minima and the measured NOE contacts was achieved by applying population-weighted averages over participating conformers based on weighted relative energies. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00404020 U6 - https://doi.org/10.1016/j.tet.2009.03.067 SN - 0040-4020 ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Fettke, Anja A1 - Kleinpeter, Erich T1 - Push-pull vs captodative aromaticity N2 - Vinylogs of fulvalenes with cyclopropenyl and cyclopentadienyl moieties attached either to different carbon atoms (c-C3H2-CH-CH=C5H4-c, 7) or to the same carbon atom [X=C(c-C3H2)(c-C5H4), 10] [X = CH2; C(CN)2; C(NH2)2; C(OCH2)2; O; c-C3H2; c-C5H4; SiH2; CCl2] of the double bond inserted between the two rings are examined theoretically at the B3LYP/ 6;311G(d,p) level. Both types of compounds are shown to possess aromaticity, which was called "push;pull" and "captodative" aromaticity, respectively. For the captodative mesoionic structures X=C(c-C3H2)(c-C5H4), the presence of both the two aromatic moieties and the C=C double bond is the necessary and sufficient condition for their existence as energetic minima on the potential energy surface. Aromatic stabilization energy (ASE) was assessed by the use of homodesmotic reactions and heats of hydrogenation. Spatial magnetic criteria (through space NMR shieldings, TSNMRS) of the two types of vinylogous fulvalenes 7 and 10 have been calculated by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept of Paul von Ragué; Schleyer, and visualized as iso-chemical-shielding surfaces (ICSS) of various sizes and directions. TSNMRS values can be successfully employed to visualize and quantify the partial push;pull and captodative aromaticity of both the three- and five-membered ring moieties. In addition, the push;pull effect in compounds 7 and 10 could be quantified by the occupation quotient ;*C=C/;C=C of the double bond inserted between the two rings. Y1 - 2008 UR - http://pubs.acs.org/loi/jpcafh U6 - https://doi.org/10.1021/jp804999m SN - 1089-5639 ER - TY - JOUR A1 - Kihampa, Charles A1 - Nkunya, Mayunga H. H. A1 - Joseph, Cosam C. A1 - Magesa, Stephen M. A1 - Hassanali, Ahmed A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich T1 - Anti-mosquito and antimicrobial nor-halimanoids, isocoumarins and an anilinoid from Tessmannia densiflora N2 - 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. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00319422 U6 - https://doi.org/10.1016/j.phytochem.2009.07.024 SN - 0031-9422 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - pi-delocalization in oligoalkynes induced by push-pull substituents and 1,3-conjugation : a combined 13C NMR and computational study ; dedicated to Prof. Alan R. Katritzky N2 - 13C chemical shifts of the push;pull oligoalkynes Don-(C;C)n-Acc (n = 1;4; Don = morpholino; Acc = COMe, COOMe) were computed at the DFT (B3LYP/6-311+G(d,p) level of theory compared with the experimental ; values and the agreement employed as a measure of quality for the underlying structures. For the global minima structures, the occupation quotients of antibonding ;* and bonding ; orbitals (;*C;C/ ;C;C) and the bond lengths (dC;C) of the various C;C triple bonds were also computed and correlated to each other. The linear dependence obtained for the two parameters dC;C and ;*C;C/ ;C;C quantifies changes in ;-delocalization induced by the push;pull effect of the substituents and 1,3-conjugation (1,3,5- and 1,3,5,7-, respectively) of the C;C bonds in the oligoalkynes studied. A critical comparison of the push;pull effect, attenuated with increasing n, and the conjugative stabilization of the oligoalkynes, increasing with n, as concluded from dC;C and ;*C;C/;C;C of the oligoalkynes and the reference compounds Me-(C;C)n-Me, Don-(C;C)n-Me, and Me-(C;C)n-Acc), respectively (Don = morpholino; Acc = COMe, COOMe), is affiliated. Y1 - 2009 UR - http://pubs.acs.org/journal/jpcafh U6 - https://doi.org/10.1021/Jp905873f SN - 1089-5639 ER - TY - JOUR A1 - Wacker, Philipp A1 - Kleinpeter, Erich T1 - Stoichiometry, complex stability, molecular size and conformational variations of metal ion crown ether complexes subject to diffusion coefficients in nonaqueous solutions N2 - Both the stoichiometry and complex stability constants of crown ether complexes with metal ions have been determined by examining gradual changes in their diffusional behavior in nonaqueous solution. Diffusion coefficients, D, were evaluated by pulsed field gradient (PFG) NMR titration experiments whilst complex stability constants were determined by nonlinear curve-fitting procedures, D versus csol., which also allow the treatment of multiple complexation equilibria (1:1 to 1:2 stoichiometries). Differences in the diffusion coefficients of the various free crown ethers with respect to their metal ion complexes indicate great sensitivity to both conformational changes and changes in molecular size upon complexation. Y1 - 2007 UR - http://www.springerlink.com/content/a584066q18q02857/ U6 - https://doi.org/10.1007/s10847-007-9332-1 ER - TY - JOUR A1 - Szatmari, Istvan A1 - Toth, Diana A1 - Koch, Andreas A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich A1 - Fulop, Ferenc T1 - Study of the substituent-influenced anomeric effect in the ring-chain tautomerism of 1-alkyl-3-aryl-naphth[1,2- e][1,3]oxazines N2 - The stabilities of the trans (B) and cis (C) tautomeric ring forms that are experimentally observed in the ring- chain tautomeric interconversion of 1-alkyl-3-aryl-2,3-dihydro-1H-naphth[1,2-e][1,3]oxazines has been investigated. Stability differences are explained by the analysis of the natural bond orbital results for the lone pairs of electrons that are on the heteroatoms in the oxazine ring system and by regression analysis of the calculated 13C NMR chemical shift values. Y1 - 2006 UR - http://onlinelibrary.wiley.com/doi/10.1002/ejoc.200600563/pdf U6 - https://doi.org/10.1002/ejoc.200600563 ER - TY - JOUR A1 - Sarodnick, Gerhard A1 - Linker, Torsten A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Starke, Ines A1 - Fürstenberg, Sylvia A1 - Kleinpeter, Erich T1 - Quinoxalines XV : convenient synthesis and structural study of pyrazolo[1,5-alpha]quinoxalines N2 - A series of aryloxymethylquinoxaline oximes, hitherto unknown and synthesized from the corresponding aldehydes, afforded in only one step pyrazolo[1,5-;]quinoxalines in the presence of acetic anhydride at high temperatures. A formal [3,5]-sigmatropic rearrangement was proposed as the mechanistic rationale for this unprecedented transformation. Saponification with potassium hydroxide furnished the free phenol derivatives which were studied by NMR spectroscopy and accompanying theoretical DFT calculations, establishing intramolecular hydrogen bonding and the spatial magnetic properties. Additionally, mass spectrometric fragmentation was investigated by B/E-linked scans and collision-induced dissociation experiments. The fragmentation pattern devoted a new gas phase rearrangement process, which proved to be unique and characteristic for pyrazolo[1,5-;]quinoxalines. Y1 - 2009 UR - http://pubs.acs.org/journal/joceah U6 - https://doi.org/10.1021/Jo802398g SN - 0022-3263 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Frank, Andrea T1 - Distinction of Push,pull effect and steric hindrance in disubstituted alkynes N2 - 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. Y1 - 2009 UR - http://www.sciencedirect.com/science/journal/00404020 U6 - https://doi.org/10.1016/j.tet.2009.03.075 SN - 0040-4020 ER - TY - JOUR A1 - Böhm, Stanislav A1 - Tomaszciková, Jana A1 - Imrich, Ján A1 - Danihel, Ivan A1 - Kristian, Pavol A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Klika, Karel D. T1 - 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 N2 - 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. Y1 - 2009 SN - 0166-1280 ER - TY - JOUR A1 - Modarresi-Alam, Ali Reza A1 - Alsadat Amirazizi, Homeyra A1 - Bagheri, Hajar A1 - Bijanzadeh, Hamid-Reza A1 - Kleinpeter, Erich T1 - Dynamic 1H NMR spectroscopic study of the ring inversion in N-sulfonyl morpholines-studies on N-S interactions N2 - 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. Y1 - 2009 SN - 0022-3263 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Frank, Andrea T1 - Quantification of the push-pull effect in substituted alkynes : evaluation of +/- I/+/- M substituent effects in terms of C C bond length variation N2 - C-13 chemical shifts of alkynes, published to date, were computed at the DFT (B3LYP/6-311G*) level of theory and compared with the experimental delta values, and the agreement was employed as a measure of quality for the underlying structures. For the corresponding global minima structures, thus obtained, the occupation quotients of antibonding pi* and bonding pi orbitals (pi*(C C)/pi(C C)) and the bond lengths (d(C C)) of the central C C triple bond were computed and correlated to each other. The linear dependence obtained for the two push-pull parameters d(C C) and pi*(C C)/pi(C C) quantifies changes in the push-pull effect of substituents while deviations from the best line of fit indicate and ascertain quantitatively to what extend the inductive (+/-l) substituent effect changes with respect to the bond length of the C C triple bond. Y1 - 2009 UR - http://pubs.acs.org/journal/jpcafh U6 - https://doi.org/10.1021/Jp9024359 SN - 1089-5639 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Szatmári, István A1 - Lázár, László A1 - Koch, Andreas A1 - Heydenreich, Matthias A1 - Fulop, Ferenc T1 - Visualization and quantification of anisotropic effects on the 1H NMR spectra of 1,3-oxazino[4,3- alpha]isoquinolines - indirect estimates of steric compression N2 - The anisotropic effects of the phenyl, alpha- and beta-naphthyl moieties in four series of 1,3-oxazino[4,3- a]isoquinolines on the H-1 chemical shifts of the isoquinoline protons were calculated by employing the Nucleus Independent Chemical Shift (NICS) concept and Visualized as anisotropic cones by a through-space NMR shielding grid. The signs and extents of these spatial effects on the H-1 chemical shifts of the isoquinoline protons were compared with the experimental H-1 NMR spectra. The differences between the experimental delta (H-1)/ppm values and the calculated anisotropic effects of the aromatic moieties are discussed in terms of the steric compression that occurs in the Compounds studied. Y1 - 2009 U6 - https://doi.org/10.1016/j.tet.2009.07.038 SN - 0040-4020 ER - TY - JOUR A1 - Fechner, Mabya A1 - Kramer, Markus A1 - Kleinpeter, Erich A1 - Koetz, Joachim T1 - Polyampholyte-modified ionic microemulsions N2 - This paper is focused on the influence of added polyampholyte, namely poly(N,N;-diallyl-N,N;- dimethyl-alt-maleamic carboxylate) on the inverse micellar phase range of the pseudo-ternary system consisting of toluene-pentanol (1:1)/SDS/water in dependence on the pH value and the temperature. Investigations on phase behavior have revealed that a greater extension in direction to the water-rich corner can be found at pH 4 compared to pH 9. In order to understand changes in the microstructure, polymer-surfactant interactions in dependence on pH have been examined by means of diffusion-ordered spectroscopy, differential scanning calorimetry, as well as conductivity measurements. The results have proven that the present microemulsion consists of water-in-oil droplets, with the polyampholyte located more in the inner core of the water droplets at pH 9 rather than at the interphase of the surfactant film at pH 4. Y1 - 2009 UR - http://www.springerlink.com/content/101551 U6 - https://doi.org/10.1007/s00396-009-2074-4 SN - 0303-402X ER - TY - JOUR A1 - Ströhl, D. A1 - Thomas, Steffen A1 - Radeglia, R. A1 - Brunn, J. A1 - Kleinpeter, Erich T1 - 13C-NMR-Untersuchungen von Substituenteneffekten in mehrfach substituierten Benz-und Naphthalenderivaten ; Inkrementberechnungen der 13C-chemischen Verschiebungen Y1 - 1992 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Hartmann, Jürgen A1 - Schroth, W. A1 - Hofer, O. A1 - Kalchhauser, H. A1 - Wurz, G. T1 - Synthesis and conformational behaviour of Ditosyldiaza[2.2]orthometacyclophanes Y1 - 1992 ER - TY - JOUR A1 - Griel, C. A1 - Ströhl, D. A1 - Jeschkeit, H. A1 - Kleinpeter, Erich T1 - Synthetische und NMR-spektroskopische Untersuchungen der Benzzyl-aminaddition an N-Maleyl- aminosäurederivaten Y1 - 1992 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Stohß, S. A1 - Schroth, W. T1 - Stereochemistry and complexational behaviour of dibenzo-crown ethers Y1 - 1992 ER - TY - JOUR A1 - Arrieta, A. A1 - Beyer, L. A1 - Lehmann, J. A1 - Dargatz, M. A1 - Kleinpeter, Erich T1 - Synthese und 1H-NMR-spektroskopische Untersuchungen neuer Curcuminanaloga Y1 - 1992 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Dargatz, M. T1 - Eine 2D-INEPT-Variante zur Detektierung wenig empfindlicher Kerne Y1 - 1992 ER - TY - BOOK A1 - Kleinpeter, Erich T1 - NMR-Spektoskopie : Struktur, Dynamik und Chemie des Moleküls Y1 - 1992 PB - Barth CY - Leipzig ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Thomas, Steffen A1 - Uhlig, G. A1 - Rudorf, Wolf-Dieter T1 - Study of the distribution of pi-Electrons in Push-Pull Alkenes by 1H an 13C NMR spectroscopy Y1 - 1993 ER - TY - JOUR A1 - Lehmann, J. A1 - Kleinpeter, Erich T1 - 1H NMR Lanthanideinduced Shift (LIS) investigations of highly flexible molecules : a new approach ; Part II Y1 - 1993 ER - TY - JOUR A1 - Lehmann, J. A1 - Kleinpeter, Erich T1 - 1H NMR Lanthanideinduced Shift (LIS) investigations of highly flexible molecules : a new approach Y1 - 1993 ER - TY - JOUR A1 - Ströhl, D. A1 - Kleinpeter, Erich T1 - Zur Stereochemie acyclischer Verbindungen : III. Bestimmung der Vorzugskonformstion unterschiedlich substituirternY-Chlorpropylether Y1 - 1993 ER -