TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Dative or coordinative carbon-boron bond in boron trapped N-heterocyclic carbenes (NHCs)? BT - an answer given on the magnetic criterion JF - Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry N2 - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of isolated as well as B-C bond length varied model compounds (BR3 trapped NHCs) have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the present dative vs. coordinative bond character of the boron-carbon bond in the trapped NHCs. Results are confirmed by bond lengths and B-11/C-13 chemical shift variations in the BR3 trapped NHCs. KW - NHCs KW - Dative vs. coordinative NHC -> BR3 bond KW - Through-space NMR KW - shieldings (TSNMRS) KW - NICS KW - Anisotropy effect Y1 - 2021 U6 - https://doi.org/10.1016/j.tet.2020.131787 SN - 0040-4020 SN - 1464-5416 VL - 80 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Koch, Andreas T1 - Identification of mesomeric substructures by through-space NMR shieldings (TSNMRS). Trimethine cyanine/merocyanine-like or aromatic pi-electron delocalization? JF - Tetrahedron N2 - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of amino-substituted heteraromatic six-membered ring systems such as pyrylium/thiopyrylium analogues have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the existing aromaticity of the studied compounds. Due to strong conjugation of six-membered ring pi-electrons and lone pairs of the exo-cyclic amino substituents (restricted rotation about partial C,N double bonds) the interplay of still aromatic and already dominating trimethine cyanine/merocyanine-like substructures can be estimated. (C) 2017 Elsevier Ltd. All rights reserved. KW - Through-space NMR shieldings (TSNMRS) KW - GIAO KW - NICS KW - Benzenoid structures KW - Cyanine/merocyanine-like structures KW - Aromaticity Y1 - 2017 U6 - https://doi.org/10.1016/j.tet.2017.05.062 SN - 0040-4020 VL - 73 SP - 4265 EP - 4274 PB - Elsevier CY - Oxford 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 - https://doi.org/10.1080/15421406.2014.949592 SN - 1542-1406 SN - 1563-5287 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 - Benzyne - an acetylene- or cumulene-like electronic structure? JF - Tetrahedron N2 - The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzyne 1 and analogues (benzene 2, 1,2,3-cyclohexatriene 3, cyclohexen-3-yne 4, cyclohexen-4-yne 5, cyclohexyne 6) have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values could be employed to compare the diatropic ring current effects of benzene and benzyne, and, when compared with the spatial magnetic properties of the analogues, to answer the question whether the benzyne electronic structure is more acetylene- or cumulene-like, supported by structural data and delta(C-13)/ppm values. (C) 2019 Published by Elsevier Ltd. KW - Benzyne-allene or cumulene-like structure KW - Trough-space NMR shieldings (TSNMRS) KW - NICS KW - Iso-chemical shielding surfaces (ICSS) KW - Ring current effect Y1 - 2019 U6 - https://doi.org/10.1016/j.tet.2019.07.011 SN - 0040-4020 VL - 75 IS - 33 SP - 4663 EP - 4668 PB - Elsevier CY - Oxford 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 - https://doi.org/10.1021/acs.jpca.5b03078 SN - 1089-5639 VL - 119 IS - 18 SP - 4268 EP - 4276 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Zborowski, Krzysztof Kazimierz A1 - Koch, Andreas A1 - Kleinpeter, Erich A1 - Proniewicz, Leonard Marian T1 - Searching for aromatic celate rings. Oxygen versus Thio and Seleno Ligands JF - Zeitschrift für physikalische Chemie : international journal of research in physical chemistry and chemical physics N2 - As a part of searching for fully aromatic chelate compounds, copper complexes of malondialdehyde as well as its sulfur and selenium derivatives were investigated using the DFT quantum chemical methods. Chelate complexes of both Cu(I) and Cu(II) ions wereconsidered. Aromaticity of the metal complexes studied were analyzed using NICS(0), NICS(1), PDI, I-ring, MCI, ICMCI and I-B aromaticity indices, and by TSNMRS visualizations of the spatial magnetic properties. It seems that partial aromaticityof studied chelates increases when oxygen atoms in malondialdehyde are replaced by sulfur and selenium. KW - Aromaticity KW - Chelatoaromaticity KW - Copper Metal Complexes KW - Quantum Chemical Calculations Y1 - 2014 U6 - https://doi.org/10.1515/zpch-2014-0528 SN - 0942-9352 VL - 228 IS - 8 SP - 869 EP - 878 PB - De Gruyter CY - Berlin 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 - https://doi.org/10.1016/j.tet.2015.02.043 SN - 0040-4020 VL - 71 IS - 15 SP - 2273 EP - 2279 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Barta, Petra A1 - Szatmari, Istvan A1 - Fueloep, Ferenc A1 - Heydenreich, Matthias A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Synthesis and stereochemistry of new naphth[1,3]oxazino[3,2-a] benzazepine and naphth[1,3]oxazino[3,2-e]thienopyridine derivatives JF - Tetrahedron N2 - Through the reactions of 1- or 2-naphthol and 4,5-dihydro-3H-benz[c]azepine or 6,7-dihydrothieno[3,2-c]pyridine, new aminonaphthol derivatives were prepared. The syntheses were extended by using N-containing naphthol analogues such as 5-hydroxyisoquinoline and 6-hydroxyquinoline. The ring closures of the novel bifunctional compounds were also achieved, resulting in new naphth[2,1-e][1,3]oxazines, naphth[1,2-e][1,3]oxazines, isoquinolino[5,6-e][1,3]oxazines and quinolino[5,6-e][1,3]oxazines. H-1 NMR spectra of the target heterocycles 16, 20 and 21 were sufficiently resolved to indentify the present stereochemistry; therefore, beside computed structures, spatial experimental (dipolar coupling-NOE) and computed (ring current effect of the naphthyl moiety-TSNMRS) NMR studies were employed. The studied heterocycles exist exclusively as S(14b),R(N), R(14b),S(N), and S(16b)S(N) isomers, respectively. The flexible moieties of the studied compounds prefer. (C) 2016 Elsevier Ltd. All rights reserved. KW - Modified Mannich reaction KW - Thienopyridine KW - Benzazepine KW - NMR spectroscopy KW - Stereochemistry KW - Theoretical calculations Y1 - 2016 U6 - https://doi.org/10.1016/j.tet.2016.03.058 SN - 0040-4020 VL - 72 SP - 2402 EP - 2410 PB - Elsevier CY - Oxford ER - TY - JOUR 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 JF - New journal of chemistry 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 CQC double bond to quantify the push-pull effect in biologically important 2-alkylidene-4-oxothiazolidines. While olefinic proton chemical shifts and differences in C-13 NMR chemical shifts of the two carbons constituting the CQC 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 ( Delta S-double dagger, Delta H-double dagger and Delta G(double dagger)), 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 Delta G(double dagger) 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 CQC bond lengths and corroborate the applicability of Delta G(double dagger) for estimation of the strength of the push-pull effect in these and related systems. Y1 - 2016 U6 - https://doi.org/10.1039/c6nj00901h SN - 1144-0546 SN - 1369-9261 VL - 40 SP - 6364 EP - 6373 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kirpichenko, Svetlana V. A1 - Kleinpeter, Erich T1 - Conformational Preferences of the Phenyl Group in 1-Phenyl-1-X-1-silacyclo-hexanes (X = MeO, HO) and 3-Phenyl-3-X-3-silatetrahydropyrans (X = HO, H) by Low Temperature C-13 NMR Spectroscopy and Theoretical Calculations JF - The journal of organic chemistry N2 - New Si-phenyl-substituted silacyclohexanes and 3-silatetrahydropyrans have been synthesized and studied with respect to the conformational equilibria of the heterosix-membered ring by low temperature C-13 NMR spectroscopy and quantum chemical calculations. For 1-methoxy-1-phenylsilacyclohexane 1 and 3-phenyl-3-silatetrahydropyran 4 the conformational equilibria could be frozen and assigned. The Ph-ax reversible arrow Ph-eq equilibrium constants at 103 K are 2.21 for 1 and 4.59 for 4. In complete agreement with former studies of similar silicon compounds, molecules 1 and 4 prefer to adopt the Pheq conformation. The conformational equilibria of 1-hydroxy-1-phenylsilacydohexane 2 and 3-hydroxy-3-phenyl-3-silatetrahydropyran 3 could not be frozen at 100 K and proved to be heavily one-sided (if not anancomeric). Obviously, there is a general trend of predominance of Phax conformer in the gas phase and of Pheq in solution. For the isolated molecules of silanols 2 and 3, calculations allowed to explain the axial predominance of the phenyl group by a larger polarization of the Si-Ph than of the Si-O bond in the Phax conformer and additional destabilization of 3-Ph-eq conformer by repulsion of unidirectional dipoles of the endocyclic oxygen lone pair and of the highly polar axial Si-O bond. Y1 - 2017 U6 - https://doi.org/10.1021/acs.joc.7b02505 SN - 0022-3263 VL - 82 SP - 13414 EP - 13422 PB - American Chemical Society CY - Washington ER -