TY - GEN
A1 - Rasovic, Aleksandar
A1 - Blagojevic, Vladimir
A1 - Baranac-Stojanovic, Marija
A1 - Kleinpeter, Erich
A1 - Markovic, Rade
A1 - Minic, Dragica M.
T1 - Quantification of the push–pull effect in 2-alkylidene-4-oxothiazolidines by using NMR spectral data and barriers to rotation around the C=C bond
N2 - Information about the strength of donor–acceptor interactions in push–pull alkenes is valuable, as this so-called “push–pull effect” influences their chemical reactivity and dynamic behaviour. In this paper, we discuss the applicability of NMR spectral data and barriers to rotation around the C[double bond, length as m-dash]C double bond to quantify the push–pull effect in biologically important 2-alkylidene-4-oxothiazolidines. While olefinic proton chemical shifts and differences in 13C NMR chemical shifts of the two carbons constituting the C[double bond, length as m-dash]C double bond fail to give the correct trend in the electron withdrawing ability of the substituents attached to the exocyclic carbon of the double bond, barriers to rotation prove to be a reliable quantity in providing information about the extent of donor–acceptor interactions in the push–pull systems studied. In particular all relevant kinetic data, that is the Arrhenius parameters (apparent activation energy Ea and frequency factor A) and activation parameters (ΔS‡, ΔH‡ and ΔG‡), were determined from the data of the experimentally studied configurational isomerization of (E)-9a. These results were compared to previously published related data for other two compounds, (Z)-1b and (2E,5Z)-7, showing that experimentally determined ΔG‡ values are a good indicator of the strength of push–pull character. Theoretical calculations of the rotational barriers of eight selected derivatives excellently correlate with the calculated C[double bond, length as m-dash]C bond lengths and corroborate the applicability of ΔG‡ for estimation of the strength of the push–pull effect in these and related systems.
T3 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 322
Y1 - 2016
U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-394523
SP - 6364
EP - 6373
ER -
TY - JOUR
A1 - Kleinpeter, Erich
A1 - Kriiger, Stefanie
A1 - Koch, Andreas
T1 - Anisotropy Effect of Three-Membered Rings in H-1 NMR Spectra: Quantification by TSNMRS and Assignment of the Stereochemistry
JF - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2 - The spatial magnetic properties (through Space NAIR shieldings, TSNMRSs) of cyclopropane; of the heteroanalogous oxirane, thiirane, and aziridine; and of various substituted dis-, and tris-cyclic analogues have been computed by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSSs) of various size and direction. The TSNMRS values, thus obtained, can be employed to visualize the anisotropy (ring current) effect of I the cyclopropane ring moiety. This approach has been employed to qualify and quantify substituent influences and contributions of appropriate ring heteroatoms O, NH, and S on the anisotropy (ring current) effect of three-mernbered ring moieties, and to assign the stereochemistry of mono-, bis-, and tris cyclic structures containing cyclopropane as a structural element. Characteristic examples are included.
Y1 - 2015
U6 - http://dx.doi.org/10.1021/acs.jpca.5b03078
SN - 1089-5639 (print)
VL - 119
IS - 18
SP - 4268
EP - 4276
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Bauer, Monika
A1 - Hartmann, Lutz
A1 - Kleinpeter, Erich
A1 - Kuschel, Frank
A1 - Pithart, Cornelia
A1 - Weissflog, Wolfgang
T1 - Chiral Dopants Derived from Ephedrine/Pseudoephedrine: Structure and Medium Effects on the Helical Twisting Power
JF - Molecular crystals and liquid crystals
N2 - Chiral dopants were obtained by acylation of enantiomerically pure ephedrine and pseudoephedrine with promesogenic carbonyl reagents. The products have been investigated with respect to their chiral transfer ability on nematic host matrices characterized by extreme differences of the dielectric anisotropy. It has been found that the medium dependence of the helicity induction nearly disappears at reduced temperatures. Based on variable temperature H-1 NMR studies on monoacylated homologues, the estimated coalescence temperatures and free activation enthalpies for the hindered rotation around C-N bonds could be correlated with the helical twisting power. Measurements by dielectric spectroscopy reveal the correlation between the molar mass of substituents linked to the chiral building block and the dynamic glass transition of corresponding chiral dopants. Furthermore, the effect of intramolecular and intermolecular hydrogen bonds has been studied by ATR-FTIR spectroscopy.
KW - ephedrine/pseudoephedrine
KW - Chiral dopants
KW - ATR-FTIR
KW - molecular structure
KW - dielectric spectroscopy
KW - H-1 NMR
Y1 - 2015
U6 - http://dx.doi.org/10.1080/15421406.2014.949592
SN - 1542-1406 (print)
SN - 1563-5287 (online)
VL - 608
IS - 1
SP - 14
EP - 24
PB - Routledge, Taylor & Francis Group
CY - Abingdon
ER -
TY - JOUR
A1 - Kleinpeter, Erich
A1 - Koch, Andreas
T1 - Characterization and quantification of quasi-aromaticity by spatial magnetic properties (TSNMRS)
JF - Tetrahedron
N2 - The spatial magnetic properties (Through Space NMR Shieldings-TSNMRS) of various types of structures with suggested quasi-aromaticity (a summaring topic: in detail push pull, captodative, chelate, supramolecular aromaticity, etc.) have been computed, are visualized as Isochemical Shielding Surfaces (ICSS) of various size/direction and examined subject to identify and quantify present (partial) aromaticity. While the TSNMRS approach proves really helpful [even in cases of (4n+2) pi-electron cyclic moieties formed via non-covalent polar interactions] quasi-aromaticity suggested for enol forms of 1,3-dicarbonyl compounds via resonance-assisted intramolecular and intermolecular hydrogen bonding cannot be confirmed. (C) 2015 Elsevier Ltd. All rights reserved.
KW - Quasi-aromaticity
KW - Ring current effect
KW - Anisotropy effect
KW - Theoretical calculations
KW - ICSS
KW - TSNMRS
Y1 - 2015
U6 - http://dx.doi.org/10.1016/j.tet.2015.06.019
SN - 0040-4020 (print)
VL - 71
IS - 33
SP - 5275
EP - 5284
PB - Elsevier
CY - Oxford
ER -
TY - JOUR
A1 - Shainyan, Bagrat A.
A1 - Kirpichenko, Svetlana V.
A1 - Chipanina, Nina N.
A1 - Oznobikhina, Larisa P.
A1 - Kleinpeter, Erich
A1 - Shlykov, Sergey A.
A1 - Osadchiy, Dmitriy Yu.
T1 - Synthesis and Conformational Analysis of 3-Methyl-3-silatetrahydropyran by GED, FTIR, NMR, and Theoretical Calculations: Comparative Analysis of 1-Hetero-3-methyl-3-silacyclohexanes
JF - The journal of organic chemistry
N2 - 3-Methyl-3-silatetrahydropyran 1 was synthesized and its molecular structure and conformational behavior was studied by gas-phase electron diffraction (GED), FTIR, low temperature H-1 and C-13 NMR spectroscopy, and by theoretical calculations (DFT, MP2). Two conformers; 1-ax and 1-eq; were located on the potential energy Surface. In the gas phase; a slight predominance of the axial conformer was determined, with the ratio 1-ax:1-eq = 54(9):46(9) (from GED) or 53:47 or 61;39 (from IR). In solution, LT NMR spectroscopy at 103 K gives the ratio 1-ax:1-eq = 35:65 (-Delta G(103)degrees = 0.13 kcal/mol). Simulation of solvent effects using the PCM continuum model or by calculation of the corresponding solvent-solute complexes allowed us to rationalize the experimentally observed opposite conformational predominance of the conformers of 3-methyl-3-silatettahydropyran in the gas phase and in solution. Comparative analysis of the effect of heteroatom in 1-hetero-3-methyl-3-silacyclohexanes on the structure, stereoelectronic interactions, and relative energies of the conformers is done.
Y1 - 2015
U6 - http://dx.doi.org/10.1021/acs.joc.5b02355
SN - 0022-3263 (print)
VL - 80
IS - 24
SP - 12492
EP - 12500
PB - American Chemical Society
CY - Washington
ER -
TY - JOUR
A1 - Shainyan, Bagrat A.
A1 - Kirpichenko, Svetlana V.
A1 - Kleinpeter, Erich
A1 - Shlykov, Sergey A.
A1 - Osadchiy, Dmitriy Yu.
T1 - Molecular structure and conformational analysis of 3-methyl-3-phenyl-3-silatetrahydropyran. Gas-phase electron diffraction, low temperature NMR and quantum chemical calculations
JF - Tetrahedron
N2 - The molecular structure and conformational behavior of 3-methyl-3-phenyl-3-silatetrahydropyran 1 was studied by gas-phase electron diffraction (GED-MS), low temperature C-13 NMR spectroscopy (LT NMR) and theoretical calculations. The 1-Ph-eq and 1-Ph-ax conformers were located on the potential energy surface. Rotation about the Si-C-ph bond revealed the phenyl ring orthogonal to the averaged plane of the silatetrahydropyran ring for 1-Ph-eq and a twisted orientation for 1-Ph-ax. Theoretical calculations and GED analysis indicate the predominance of 1-Ph-ax in the gas phase with the ratio of conformers (GED) 1-Ph-eq:1-Ph-ax=38:62 (Delta G degrees(307)=-0.29 kcal/mol). In solution, LT NMR spectroscopy gives almost the opposite ratio Ph-eq:1-Ph-ax=68:32 (Delta G degrees(103)=0.16 kcal/mol). Simulation of solvent effects using the PCM continuum model or by calculation of the solvent-solute complexes allowed us to rationalize the experimentally observed opposite conformational predominance of the conformers of compound 1 in the gas phase and in solution. (C) 2015 Elsevier Ltd. All rights reserved.
KW - 3-Silatetrahydropyrans
KW - Conformational analysis
KW - Low temperature NMR spectroscopy
KW - Gas-phase electron diffraction
KW - Quantum chemical calculations
Y1 - 2015
U6 - http://dx.doi.org/10.1016/j.tet.2015.03.117
SN - 0040-4020 (print)
VL - 71
IS - 23
SP - 3810
EP - 3818
PB - Elsevier
CY - Oxford
ER -
TY - JOUR
A1 - Shainyan, Bagrat A.
A1 - Kirpichenko, Svetlana V.
A1 - Kleinpeter, Erich
T1 - Stereochemistry of 3-isopropoxy-3-methyl-1,3-oxasilinane-the first 3-silatetrahydropyran with an exo-cyclic RO-Si bond
JF - Tetrahedron
N2 - Molecular structure and conformational behavior of 3-isopropoxy-3-methyl-3-oxasilinane is studied by low temperature C-13 NMR spectroscopy and theoretical calculations (DFT, MP2). Two conformers, 1-ROax and 1-ROeq, were found experimentally and located on the potential energy surface. LT C-13 NMR spectroscopy gives almost equal population of the two conformers at 98 K with Delta G(98K)degrees=0.02 kcal/mol in favor of 1-ROax and Delta G(98K)(#)=4.5 kcal/mol. The corresponding DFT calculated values (Delta G(98K)degrees=0.03 kcal/mol, Delta G(98K)(#)=5.1 kcal/mol) are in excellent agreement with the experiment. Detailed DFT and MP2 calculations of the solvent effect on the conformational equilibrium were performed and highlighted the leveling out of the two conformers when transferred from gas to solution. (C) 2015 Published by Elsevier Ltd.
KW - 1,3-Oxasilinanes
KW - Conformational equilibrium
KW - Barrier to ring inversion
KW - Solvent effects
KW - Assignment of stereochemistry
Y1 - 2015
U6 - http://dx.doi.org/10.1016/j.tet.2015.07.047
SN - 0040-4020 (print)
VL - 71
IS - 38
SP - 6720
EP - 6726
PB - Elsevier
CY - Oxford
ER -
TY - JOUR
A1 - Kleinpeter, Erich
A1 - Michaelis, Marcus
A1 - Koch, Andreas
T1 - Are para-nitro-pyridine N-oxides quinonoid or benzenoid? An answer given by spatial NICS (TSNMRS)
JF - Tetrahedron
N2 - The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of a number of substituted para-nitro-pyridine N-oxides have been computed, visualized as Iso-Chemical-Shielding-Surfaces (ICSS) of various size and direction, and were examined subject to the present quinonoid or benzenoid pi-relectron distribution of the six-membered ring. (C) 2015 Elsevier Ltd. All rights reserved.
KW - para-Nitro-pyridine N-oxides
KW - Quinonoid structure
KW - Benzenoid structure
KW - Ring current effect
KW - Anisotropy effect
KW - Theoretical calculations
Y1 - 2015
U6 - http://dx.doi.org/10.1016/j.tet.2015.02.043
SN - 0040-4020 (print)
VL - 71
IS - 15
SP - 2273
EP - 2279
PB - Elsevier
CY - Oxford
ER -
TY - JOUR
A1 - Kolocouris, Antonios
A1 - Koch, Andreas
A1 - Kleinpeter, Erich
A1 - Stylianakis, Ioannis
T1 - 2-Substituted and 2,2-disubstituted adamantane derivatives as models for studying substituent chemical shifts and C-H-ax center dot center dot center dot Y-ax cyclohexane contacts-results from experimental and theoretical NMR spectroscopic chemical shifts and DFT structures
JF - Tetrahedron
N2 - The complete H-1 and C-13 NMR chemical shifts assignment for various 2-substituted and 2,2-disubstituted adamantane derivatives 1-38 in CDCl3 solution was realized on the basis of NMR experiments combined with chemical structure information and DFT-GIAO (B3LYP/6-31+G(d,p)-GIAO) calculations of chemical shifts in solution. Substituent-induced C-13 NMR chemical shifts (SCS) are discussed. C-H-ax center dot center dot center dot Y-ax contacts are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts will be further investigated in this work on basis of new adamantane derivatives, which are substituted at C-2 to provide models for 1,4-C-H-ax center dot center dot center dot Y-ax and 1,5-C-H-ax center dot center dot center dot Y-ax contacts. The B3LYP/6-31+G(d,p) calculations predicted the presence of NBO hyperconjugative attractive interactions between C-H-ax and Y-ax groups along C-H-ax center dot center dot center dot Y-ax contacts. The H-1 NMR signal separation, Delta delta(gamma-CH2), reflects the strength of the H-bonded C-H-ax center dot center dot center dot Y-ax contact. (C) 2015 Elsevier Ltd. All rights reserved.
KW - 2-Substituted adamantane derivatives
KW - 2,2-Disubstituted adamantane derivatives
KW - H-1 NMR
KW - C-13 NMR
KW - B3LYP/6-31+G(d,p) calculations
KW - GIAO calculations
KW - Substituent chemical shifts
Y1 - 2015
U6 - http://dx.doi.org/10.1016/j.tet.2015.01.044
SN - 0040-4020 (print)
VL - 71
IS - 16
SP - 2463
EP - 2481
PB - Elsevier
CY - Oxford
ER -
TY - JOUR
A1 - Kleinpeter, Erich
A1 - Koch, Andreas
A1 - Schulz, Stefanie
A1 - Wacker, Philipp
T1 - Interplay of para- and diatropic ring currents [(anti)aromaticity] of macrocyclic rings subject to conformational influences, further annelation and hydrogenation of aromatic ring moieties
JF - Tetrahedron
N2 - The spatial magnetic properties (Through Space NMR Shieldings-TSNMRS) of a variety of porphyrins, hemiporphyrazines and tetraoxo[8]circulenes have been computed, visualized as Iso-chemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to the interplay of present (para)-diatropic ring currents [(anti)aromaticity] and influences on the latter property originating from the macrocyclic ring conformation, further annelation and partial to complete hydrogenation of aromatic ring moieties. Caution seems to be indicated when concluding from a single NICS parameter to present (para)diatropic ring currents [(anti)aromaticity]. (C) 2014 Elsevier Ltd. All rights reserved.
KW - Porphyrins
KW - Hemiporphyrazines
KW - Tetraoxo[8]circulenes
KW - (Anti)aromaticity
KW - Anisotropy effect
KW - Theoretical calculations
Y1 - 2014
U6 - http://dx.doi.org/10.1016/j.tet.2014.10.018
SN - 0040-4020 (print)
VL - 70
IS - 48
SP - 9230
EP - 9239
PB - Elsevier
CY - Oxford
ER -