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 - 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 - 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 - https://doi.org/10.1016/j.tet.2014.10.018 SN - 0040-4020 VL - 70 IS - 48 SP - 9230 EP - 9239 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Klaumuenzer, Ute T1 - Quantification of the push-pull Effect in disubstituted alkynes - Application of occupation quotients pi*/pi and C-13 chemical shift differences Delta delta(C C) JF - Journal of molecular structure N2 - Structures, C-13 chemical shifts, and the occupation quotients of anti-bonding pi* and bonding pi orbitals of the C C triple bond along a series of push-pull alkynes (p)X-C6H4 C(O)-C C-NH-C6H4-Y(P) (X,Y= H, Me, OMe, NMe2, NO2, COMe, COOMe, F, Cl, Br) were computed at the DFT level (B3LYP/6-311G**) of theory. Both the stereochemistry (cis/trans-isomers) by steric twist and the push-pull character by both C-13 chemical shift differences (Delta delta(C C)) and the occupation quotient (pi(C C)/pi(C C)) were studied; the latter two parameters can be readily employed to precisely quantify the push-pull effect in alkynes. (C) 2014 Elsevier B.V. All rights reserved. KW - Push-pull effect KW - C-13 chemical shift difference Delta delta(C C) KW - Occupation quotient pi*/pi KW - Push-pull alkynes KW - Steric hindrance Y1 - 2014 U6 - https://doi.org/10.1016/j.molstruc.2014.05.072 SN - 0022-2860 SN - 1872-8014 VL - 1074 SP - 193 EP - 195 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Moskalik, Mikhail Yu A1 - Heydenreich, Matthias A1 - Kleinpeter, Erich T1 - Conformational equilibrium and dynamic behavior of bis-N-triflyl substituted 3,8-diazabicyclo[3.2.1]octane JF - Magnetic resonance in chemistry N2 - Restricted rotation about the N-S partial double bonds in a bis-N-triflyl substituted 3,8-diazabicyclo[3.2.1]octane derivative 1 has been frozen at low temperature (Delta G* = 11.6 kcal mol(-1)), and the existence of all four rotamers about the two N-S bonds, 3-in, 8-in, 3-in, 8-out, 3-out, 8-in, and 3-out, 8-out, respectively, proved experimentally by NMR spectroscopy and theoretically by DFT and MP2 calculations. Copyright (C) 2014 John Wiley & Sons, Ltd. KW - NMR KW - H-1 KW - C-13 KW - F-19 KW - Dynamic NMR KW - Conformational equilibrium KW - restricted N-S rotation Y1 - 2014 U6 - https://doi.org/10.1002/mrc.4086 SN - 0749-1581 SN - 1097-458X VL - 52 IS - 8 SP - 448 EP - 452 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Kleinpeter, Erich T1 - Conformational flexibility of 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline and its monoheterocyclic analogs JF - Russian journal of general chemistry N2 - Conformational behavior of the first cyclic organosilicon vinylsulfide, 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline as well as its monoheterocyclic analogs, 3,4-dihydro-2H-pyran, 3,4-dihydro-2H-thiopyran, and 1,1-dimethyl-1,2,3,4-tetrahydrosiline is studied in comparison with the carbocyclic analog, cyclohexene, using the methods of low-temperature NMR spectroscopy and theoretical calculations at the DFT and MP2 levels of theory. The barrier to the ring inversion with respect to that in cycloxene is increased in 3,4-dihydro-2H-pyran and 1,1-dimethyl-1,2,3,4-tetrahydrosiline, but, in contrast to the suggestions made in the literature, is decreased in 3,4-dihydro-2H-thiopyran. In 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline the barrier is intermediate between those in the corresponding monoheterocycles, 1,1-dimethyl-1,2,3,4-tetrahydrosiline and 3,4-dihydro-2H-thiopyran. The observed variations are rationalized from the viewpoint of the interaction of the pi-electrons of the C=C double bond with the orbitals of heteroatoms in the ring. The structure of the transition state for the ring inversion is discussed. KW - 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline KW - 1,1-dimethyl-1,2,3,4-tetrahydrosiline KW - 3,4-dihydro-2H-thiopyran KW - 3,4-dihydro-2H-pyran KW - onformational analysis Y1 - 2014 U6 - https://doi.org/10.1134/S1070363214070135 SN - 1070-3632 SN - 1608-3350 VL - 84 IS - 7 SP - 1325 EP - 1329 PB - Pleiades Publ. CY - New York ER - TY - JOUR A1 - Kleinpeter, Erich ED - Webb, GA T1 - Quantification and visualization of the anisotropy effect in NMR spectroscopy by through-space NMR shieldings JF - Annual reports on NMR spectroscopy JF - Annual Reports on NMR Spectroscopy N2 - The anisotropy effect of functional groups (respectively the ring-current effect of aryl moieties) in H-1 NMR spectra has been computed as spatial NICS (through-space NMR chemical shieldings) and visualized by iso-chemical-shielding surfaces of various size and low(high) field direction. Hereby, the anisotropy/ring-current effect, which proves to be the molecular response property of spatial NICS, can be quantified and can be readily employed for assignment purposes in proton NMR spectroscopy-characteristic examples of stereochemistry and position assignments (the latter in supramolecular structures) will be given. In addition, anisotropy/ring-current effects in H-1 NMR spectra can be quantitatively separated from the second dominant structural effect in proton NMR spectra, the steric compression effect, pointing into the reverse direction, and the ring-current effect, by far the strongest anisotropy effect, can be impressively employed to visualize and quantify (anti) aromaticity and to clear up standing physical-organic phenomena as are pseudo-, spherical, captodative, homo-and chelatoaromaticity, to characterize the pi-electronic structure of, for example, fulvenes, fulvalenes, annulenes or fullerenes and to differentiate aromatic and quinonoid structures. KW - Through-space NMR shielding (TSNMRS) KW - Anisotropy effect KW - Stereochemistry KW - Ring-current effect KW - Aromatic or quinonoid KW - Aromaticity KW - Chelatoaromaticity KW - Binding pocket position KW - Supramolecular compounds KW - Diastereomers assignment Y1 - 2014 SN - 978-0-12-800184-4 U6 - https://doi.org/10.1016/B978-0-12-800184-4.00003-5 SN - 0066-4103 VL - 82 SP - 115 EP - 166 PB - Elsevier CY - San Diego 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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? JF - Arkivoc : free online journal of organic chemistry 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. KW - Through-space NMR shieldings (TSNMRS) KW - GIAO KW - NICS KW - benzenoid structures KW - quinoid structures KW - aromaticity Y1 - 2012 SN - 1551-7004 SP - 94 EP - 108 PB - ARKAT CY - Gainesville 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 -