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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - 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  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Intramolecular carbene stabilization via 3c,2e bonding on basis of 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 bent cyclobutylcarbene 8, 1,2-diboretane-3-ylidene 9, and some carbene analogues of boron 14-18 as most intriguing examples of carbenes, which can be stabilized as homoaromatic systems with 3c,2e bonding, 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, ring current effect/anisotropy effects as measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the degree of present 3c,2e-homoaromaticity. Results are confirmed by geometry (bond angles and bond lengths) and spectroscopic data, the delta(B-11)/ppm data and the C-13 chemical shifts of the carbene electron-deficient centre.
KW  - Cyclobutylcarbene
KW  - 1,2-diboretane-3-ylidene
KW  - 3c,2e-bonding
KW  - Through-space NMR shieldings (TSNMRS)
KW  - NICS
Y1  - 2021
U6  - https://doi.org/10.1016/j.tet.2021.132357
SN  - 0040-4020
SN  - 1464-5416
VL  - 95
PB  - Elsevier Science
CY  - Amsterdam
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  - https://doi.org/10.1016/j.tet.2015.06.019
SN  - 0040-4020
VL  - 71
IS  - 33
SP  - 5275
EP  - 5284
PB  - Elsevier
CY  - Oxford
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
JF  - Tetrahedron
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 H-1 and C-13 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.
KW  - 4-Substituted cyclohexanones
KW  - Conformational analysis
KW  - Dynamic NMR
KW  - Simulation of H-1 NMR spectra
KW  - Quantum chemical calculations
KW  - ALTONA equation
Y1  - 2012
U6  - https://doi.org/10.1016/j.tet.2012.01.022
SN  - 0040-4020
VL  - 68
IS  - 10
SP  - 2363
EP  - 2373
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Neuvonen, Kari
A1  - Neuvonen, Helmi
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - Taft equation in the light of NBO computations introduction of a novel polar computational substituent constant scale sigma(q)* for alkyl groups
JF  - Computational and theoretical chemistry
N2  - The validity of the Taft equation: log(k(R)/k(CH3)) = rho*sigma* + delta E-S was studied with the aid of NBO computational results concerning cyclohexyl esters RCOOC6H11 [R = Methyl, Ethyl, n-Propyl, Isopropyl, n-Butyl, Isobutyl, sec-Butyl, tert-Butyl, Neopentyl, CH(CH2CH3)(2), CH(CH3)C(CH3)(3), C(CH3)(2)CH2CH3, C(CH3)(2)C(CH3)(3), CH(CH3)(Np), CH(iPr)(tBu), C(Me)(Et)(iPr), C(Et)(2)(tBu) or C(Et)(iPr)(tBu)]. It was proved that the sigma*(alkyl) value is a composite substitutent constant including the polar and steric contributions. A novel computational sigma(q)* substituent constant scale is presented based on the NBO atomic charges of the alpha-carbon and the computational total steric exchange energies E(ster) of the cyclohexyl esters specified above. The method used offers a useful way to calculate sigma*(alkyl) values for alkyl groups for which experimental Taft's polar sigma* parameters are not available.
KW  - NBO analysis
KW  - Taft equation
KW  - Polar substituent constant
KW  - Steric effect
Y1  - 2012
U6  - https://doi.org/10.1016/j.comptc.2011.11.044
SN  - 2210-271X
VL  - 981
IS  - 2
SP  - 52
EP  - 58
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Balci, Kubilay
A1  - Yapar, G.
A1  - Akkaya, Y.
A1  - Akyuz, S.
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - A conformational analysis and vibrational spectroscopic investigation on 1,2-bis(o-carboxyphenoxy) ethane molecule
JF  - Vibrational spectroscopy : an international journal devoted to applications of infrared and raman spectroscopy
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 contribution 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 vibrations to conformation, substitution and dimerization were discussed.
KW  - Glycol podands
KW  - Salicylic acid
KW  - IR and Raman spectra
KW  - SQM FF
KW  - Dual Scale Factors
Y1  - 2012
U6  - https://doi.org/10.1016/j.vibspec.2011.11.011
SN  - 0924-2031
VL  - 58
IS  - 1-2
SP  - 27
EP  - 43
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Baranac-Stojanovic, Marija
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - Is the conventional interpretation of the anisotropic effects of C=C double bonds and aromatic rings in NMR spectra in terms of the p-electron shielding/deshielding contributions correct?
JF  - Chemistry - a European journal
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 angstrom 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 p-electron shielding/deshielding effects. In fact, these effects followed the predictions only for the antiaromatic cyclobutadiene ring.
KW  - ab initio calculations
KW  - anisotropic effects
KW  - NMR spectroscopy
KW  - nucleus-independent chemical shift
KW  - pi interactions
Y1  - 2012
U6  - https://doi.org/10.1002/chem.201101882
SN  - 0947-6539
VL  - 18
IS  - 1
SP  - 370
EP  - 376
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
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)
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
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
U6  - https://doi.org/10.1039/c2cp40501f
SN  - 1463-9076
VL  - 14
IS  - 24
SP  - 8742
EP  - 8746
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Csuetoertoeki, Renata
A1  - Szatmari, Istvan
A1  - Koch, Andreas
A1  - Heydenreich, Matthias
A1  - Kleinpeter, Erich
A1  - Fueloep, Ferenc
T1  - Synthesis and conformational analysis of new naphth[1,2-e][1,3]oxazino[3,4-c]quinazoline derivatives
JF  - Tetrahedron
N2  - A new highly functionalized aminonaphthol derivative, 1-(amino(2-aminophenyl)methyl)-2-naphthol (4), was synthesized by the reaction of 2-naphthol, 2-nitrobenzaldehyde and tert-butyl carbamate or benzyl carbamate, followed by reduction and/or removal of the protecting group. The aminonaphthol derivative thus obtained was converted in ring-closure reactions with formaldehyde. benzaldehyde and/or phosgene to the corresponding naphth[1,2-e][1,3]oxazino[3,4-c]quinazoline derivatives. The conformational analysis of some derivatives by NMR spectroscopy and accompanying molecular modelling are also reported.
KW  - Naphthoxazinoquinazolines
KW  - NMR
KW  - Conformational analysis
KW  - DFT calculations
KW  - Hammett-Brown plots
Y1  - 2011
U6  - https://doi.org/10.1016/j.tet.2011.08.074
SN  - 0040-4020
VL  - 67
IS  - 44
SP  - 8564
EP  - 8571
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Pihlaja, Kalevi
A1  - Sinkkonen, Jari
A1  - Stajer, Geza
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - 1-Oxo-1,3-dithiolanes - synthesis and stereochemistry
JF  - Magnetic resonance in chemistry
N2  - 1-Oxo-1,3-dithiolane (4) and its cis- and trans-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 NaIO(4) in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with (1)H and (13)C NMR spectroscopy and molecular modelling. The sulfoxides 4-6 and 8-10 attain two S(1) type envelopes (sometimes slightly distorted) the S=O(ax) envelope greatly dominating. Cis-4-methyl-1-oxo-1,3-dithiolane is a special case exhibiting both two closely related S=O(ax) (30 and 27%) as well as S=O(eq) (21 and 22%) forms [S(1) and C(4) envelopes, respectively]. The relative energies of these conformations, the values of (1)H-(1)H coupling constants and (1)H and (13)C chemical shifts were estimated by computational methods and they support well the conclusions based on the experimental data.
KW  - NMR
KW  - (1)H NMR
KW  - (13)C NMR
KW  - sulfur heterocycles
KW  - conformational analysis
KW  - computational chemistry
Y1  - 2011
U6  - https://doi.org/10.1002/mrc.2764
SN  - 0749-1581
VL  - 49
IS  - 7
SP  - 443
EP  - 449
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - The anisotropic effect of functional groups in H-1 NMR spectra is the molecular response property of spatial NICS-the frozen conformational equilibria of 9-arylfluorenes
JF  - Tetrahedron
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 substituents are consequently positioned either above the fluorene moiety or in-plane with it; thus, the methyl protons are either shielded or deshielded, respectively, due to the ring current effect of the fluorene moiety. This anisotropic effect on the H-1 chemical shifts of the methyl protons has been quantified on the basis of through-space NMR shieldings (TSNMRS) and subsequently Delta delta(calcd) compared with the experimentally observed chemical shift differences, Delta delta(exp). In this context, the experimental anisotropic effects of functional groups in the H-1 NMR have proven to quantitatively be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS). Differences between Delta delta(calcd) and Delta delta(exp) were, for the first time, also quantified as arising from steric compression.
KW  - Through-space NMR shieldings (TSNMRS)
KW  - Spatial NICS
KW  - Anisotropic effect
KW  - Iso-chemical-shielding surfaces (ICSS)
KW  - 9-Arylfluorenes
Y1  - 2011
U6  - https://doi.org/10.1016/j.tet.2011.06.005
SN  - 0040-4020
VL  - 67
IS  - 32
SP  - 5740
EP  - 5743
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Neuvonen, Kari
A1  - Neuvonen, Helmi
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - NBO analysis of polar and steric effect using the axial-equatorial equilibrium of cyclohexyl acetates as a probe
JF  - Computational and theoretical chemistry
N2  - The proportion of the axial conformer increases in the ax reversible arrow eq equilibrium of cyclohexyl acetates (RCOOC(6)H(11), R reversible arrow Me, Et, iPr, tBu, CH(2)Cl, CHCl(2), CO(3). CH(2)Br, CHBr(2), CBr(3)) with the increasing size of the acyloxy substitution. The nature of this unexpected steric substituent effect, which is opposite to general stereochemical concepts, was studied by means of ab kiln MO method, accompanied by NBO and isodesmic calculations. NBO parameters seem to be good descriptors for quantitative prediction of the experimental Delta G degrees value of the title conformational equilibrium. The origin and propagation of the substituent effect of the polar substitutions (CH(2)Cl, CHCl(2), CCl(3), CH(2)Br, CHBr(2), CBr(3)) differ, however, from those of the pure alkyl (Me, Et, iPr, tBu) substitutions. The Delta G degrees value of the polar derivatives depends on the qC8 charges, on the occupation of the sigma(center dot)(C1-07) orbital and on the hyperconjugative pi(center dot)(c=O) -> sigma(center dot)(C10-X) and sigma(center dot)(C10-X) -> pi(center dot)(c=O) interactions. The substituent sensitivity of these NBC parameters for the two conformers differ to the effect that the ax reversible arrow eq equilibrium is shifted to the left side with increasing electron withdrawing character of the acyloxy group. The Delta G degrees values of the alkyl derivatives are interpreted in terms of the calculated dipole moments. The destabilization in the non-polar medium (the experimental Delta G degrees values used were measured in CD(2)Cl(2)) due to the enhanced dipolar character is more prominent in the case of the equatorial alkyl conformers. As the consequence, the ax reversible arrow eq equilibrium is shifted to the left despite the increasing size of the R group when going from Me to tBu substitution.
KW  - Substituent effects
KW  - Ab initio MO computations
KW  - Conformational equilibria
KW  - Cyclohexyl esters
KW  - NBO analysis
Y1  - 2011
U6  - https://doi.org/10.1016/j.comptc.2010.12.033
SN  - 2210-271X
VL  - 964
IS  - 1-3
SP  - 234
EP  - 242
PB  - Elsevier
CY  - Amsterdam
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)
JF  - Physical chemistry, chemical physics : a journal of European Chemical Societies
N2  - The spatial magnetic properties (through space NMR shieldings-TSNMRS) of metal complexes (with ligands such as acetylacetone, 3-hydroxy-pyran(4) one) and "metallobenzenes" have been calculated by the GIAO perturbation method and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various sizes and directions. The TSNMRS values, thus obtained, can be successfully employed to quantify and visualize partial aromaticity of the metallocyclic ring by comparison with the spatial magnetic properties of the corresponding non-complexed ligands in comparable structural and electronic situations, and benzene, respectively. Because anisotropy/ring current effects in H-1 NMR spectra proved to be the molecular response property of TSNMRS, the results obtained concerning partial "chelatoaromaticity" are experimentally ensured.
Y1  - 2011
U6  - https://doi.org/10.1039/c1cp21942a
SN  - 1463-9076
SN  - 1463-9084
VL  - 13
IS  - 46
SP  - 20593
EP  - 20601
PB  - Royal Society of Chemistry
CY  - Cambridge
ER  - 
TY  - JOUR
A1  - Hansen, Poul Erik
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - Ring current and anisotropy effects on OH chemical shifts in resonance-assisted intramolecular H-bonds
JF  - Tetrahedron letters
N2  - Ring current effects on resonance-assisted and intramolecularly bridged hydrogen bond protons for 10-hydroxybenzo[h]quinoline 1 and a number of related compounds were calculated and the through-space NMR shieldings (TSNMRS) obtained hereby visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. These calculations revealed that this through-space effect is comparably large (up to 2 ppm) dependent on the position of the intramolecularly bridged OH proton, and therefore, contribute considerably to the chemical shift of the latter making it questionable to use delta(OH)/ppm in the estimation of intramolecular hydrogen bond strength without taking this into account. Furthermore, the anisotropy effects of additional groups on the aromatic moiety (e.g. the carbonyl group in salicylaldehyde or in o-hydroxyacetophenone of ca. 0.6 ppm deshielding) should also be considered. These through-space effects need to be taken into account when using OH chemical shifts to estimate hydrogen bond strength.
KW  - RA-intramolecular hydrogen bond
KW  - Through-space NMR shieldings (TSNMRS)
KW  - Iso-chemical-shielding surfaces (ICSS)
KW  - Ring current effect
KW  - Anisotropy effect
Y1  - 2018
U6  - https://doi.org/10.1016/j.tetlet.2018.05.006
SN  - 0040-4039
VL  - 59
IS  - 23
SP  - 2288
EP  - 2292
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Buyinza, Daniel
A1  - Derese, Solomon
A1  - Ndakala, Albert
A1  - Heydenreich, Matthias
A1  - Yenesew, Abiy
A1  - Koch, Andreas
A1  - Oriko, Richard
T1  - A coumestan and a coumaronochromone from Millettia lasiantha
JF  - Biochemical systematics and ecology
N2  - The manuscript describes the phytochemical investigation of the roots, leaves and stem bark of Millettia lasiantha resulting in the isolation of twelve compounds including two new isomeric isoflavones lascoumestan and las-coumaronochromone. The structures of the new compounds were determined using different spectroscopic techniques.
KW  - Millettia lasiantha
KW  - Leguminosae
KW  - Coumestan
KW  - Coumaronochromone
Y1  - 2021
U6  - https://doi.org/10.1016/j.bse.2021.104277
SN  - 0305-1978
SN  - 1873-2925
VL  - 97
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Cyclazines-structure and aromaticity or antiaromaticity on the magnetic criterion
JF  - European journal of organic chemistry
N2  - Structure and spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of all ten cycl[2.2.2]azine to cycl[4.4.4]azine, hetero-analogues and the corresponding hydrocarbons have been calculated at the B3LYP/6-311G(d,p) theory level using the GIAO perturbation method and employing the nucleus independent chemical shift (NICS) concept. The TSNMRS values (actually, the ring current effect as measurable in H-1 NMR spectroscopy) are visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction, and employed to readily qualify and quantify the degree of (anti)aromaticity. Results are confirmed by NMR [delta(H-1)/ppm, delta(N-15)/ppm] and geometry (planar, twisted, bow-shaped) data. The cyclazines N[2.2.2](-) up to N[2.4.4](-) are planar or at most slightly bowl-shaped and, due to coherent peripheral ring currents (except in N[2.3.3](-), N[2.3.4], N[3.3.4](+) and N[2.4.4](+)), develop aromaticity or anti-aromaticity of the whole molecules dependent on the number of peripheral conjugated pi electrons. The cyclazines N[2.3.3](-), N[2.3.4], N[3.3.4](+) and N[2.4.4](+) develop two ring currents of different direction within the same molecule, in which the dominating ring current proves to be paratropic (in N[3.3.4](+) diatropic) including the nodal N p(z) lone pair into the conjugation. The residual cyclazines N[3.4.4], N[4.4.4](-) and N[4.4.4](+) are heavily twisted and, therefore, are not developing peripheral or diverse ring currents. The TSNMRS information about cyclazines and the parent tricyclic annulene analogues is congruent subject to structure and number of peripheral or internal conjugated pi electrons, the corresponding (anti)aromaticity is in unequivocal accordance with Huckel's rule.
KW  - Aromaticity
KW  - Cyclazines
KW  - NMR spectroscopy
KW  - Peripheral ring current
Y1  - 2022
U6  - https://doi.org/10.1002/ejoc.202101362
SN  - 1434-193X
SN  - 1099-0690
VL  - 2022
IS  - 8
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Balci, K.
A1  - Akkaya, Y.
A1  - Akyuz, S.
A1  - Collier, W. B.
A1  - Stricker, M. C.
A1  - Stover, D. D.
A1  - Ritzhaupt, G.
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
T1  - The effects of conformation and zwitterionic tautomerism on the structural and vibrational spectral data of anserine
JF  - Vibrational spectroscopy : an international journal devoted to applications of infrared and raman spectroscopy
N2  - In this study, the stable conformers of neutral anserine were searched by molecular dynamics simulations and energy minimization calculations using the MM2 force field. Thermochemical calculations at B3LYP/6-31G(d) level of theory followed these preliminary calculations. The results confirmed that neutral anserine has quite a flexible structure and many stable gauche and trans conformers at room temperature. Nevertheless, two are considerably more favourable in energy than the others and expected to dominate the gas-phase and matrix IR spectra of the molecule. The corresponding structural and vibrational spectral data for these two conformers of neutral anserine, whose relative stabilities were also examined by high-accuracy energy calculations carried out using G3MP2B3 method, and for the most stable conformer of anserine in zwitterion form were calculated at B3LYP/6-311++G(d,p) level of theory. The calculated harmonic force constants were refined using the Scaled Quantum Mechanical Force Field (SQM-FF) method and then used to produce the refined wavenumbers, potential energy distributions (PEDs) and IR and Raman intensities. These refined data together with the scaled harmonic wavenumbers obtained using another method, Dual Scale factors (DS), enabled us to correctly analyse the observed IR and Raman spectra of anserine and revealed the effects of conformation and zwitterionic tautomerism on its structural and vibrational spectral data. (C) 2016 Elsevier B.V. All rights reserved.
KW  - Anserine
KW  - Matrix IR spectrum
KW  - Tautomerism
KW  - SQM-FF
KW  - Dual scale factors
Y1  - 2016
U6  - https://doi.org/10.1016/j.vibspec.2016.08.003
SN  - 0924-2031
SN  - 1873-3697
VL  - 86
SP  - 277
EP  - 289
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - The 13 C chemical shift and the anisotropy effect of the carbene electron-deficient centre
BT  - simple means to characterize the electron distribution of carbenes
JF  - Magnetic resonance in chemistry
N2  - Both the C-13 chemical shift and the calculated anisotropy effect (spatial magnetic properties) of the electron-deficient centre of stable, crystalline, and structurally characterized carbenes have been employed to unequivocally characterize potential resonance contributors to the present mesomerism (carbene, ylide, betaine, and zwitter ion) and to determine quantitatively the electron deficiency of the corresponding carbene carbon atom. Prior to that, both structures and C-13 chemical shifts were calculated and compared with the experimental delta(C-13)/ppm values and geometry parameters (as a quality criterion for obtained structures).
KW  - C-13 chemical shift
KW  - carbenes
KW  - zwitterions
KW  - carbene electron deficiency
KW  - nucleus-independent chemical shifts (NICS)
KW  - through space NMR shieldings
KW  - (TSNMRS)
Y1  - 2019
U6  - https://doi.org/10.1002/mrc.4979
SN  - 0749-1581
SN  - 1097-458X
VL  - 58
IS  - 3
SP  - 280
EP  - 292
PB  - Wiley
CY  - Hoboken
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  - https://doi.org/10.1016/j.tet.2015.01.044
SN  - 0040-4020
VL  - 71
IS  - 16
SP  - 2463
EP  - 2481
PB  - Elsevier
CY  - Oxford
ER  - 
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  - 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  - Kleinpeter, Erich
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Krtitschka, Angela
A1  - Krüger, Tobias
A1  - Linker, Torsten
T1  - NMR spectroscopic conformational analysis of 4-methylene-cyclohexyl pivalateThe effect of sp(2) hybridization
JF  - Magnetic resonance in chemistry
N2  - The conformational equilibrium of the axial/equatorial conformers of 4-methylene-cyclohexyl pivalate is studied by dynamic NMR spectroscopy in a methylene chloride/freon mixture. At 153K, the ring interconversion gets slow on the nuclear magnetic resonance timescale, the conformational equilibrium (-G degrees) can be examined, and the barrier to ring interconversion (G(#)) can be determined. The structural influence of sp(2) hybridization on both G degrees and G(#) of the cyclohexyl moiety can be quantified.
KW  - 4-methylene-cyclohexyl pivalate
KW  - conformational analysis
KW  - dynamic NMR spectroscopy
KW  - exo-methylene conformational effect at cyclohexane
KW  - quantum chemical calculations
Y1  - 2017
U6  - https://doi.org/10.1002/mrc.4630
SN  - 0749-1581
SN  - 1097-458X
VL  - 55
SP  - 1073
EP  - 1078
PB  - Wiley
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Szatmari, Istvan
A1  - Belasri, Khadija
A1  - Heydenreich, Matthias
A1  - Koch, Andreas
A1  - Kleinpeter, Erich
A1  - Fulop, Ferenc
T1  - Ortho-Quinone methide driven synthesis of new O,N- or N,N-Heterocycles
JF  - ChemistryOpen : including thesis treasury
N2  - To synthesize functionalized Mannich bases that can serve two different types of ortho-quinone methide (o-QM) intermediates, 2-naphthol and 6-hydroxyquinoline were reacted with salicylic aldehyde in the presence of morpholine. The Mannich bases that can form o-QM and aza-o-QM were also synthesized by mixing 2-naphthol, 2-nitrobenzaldehyde, and morpholine followed by reduction of the nitro group. The highly functionalized aminonaphthol derivatives were then tested in [4+2] cycloaddition with different cyclic imines. The reaction proved to be both regio- and diastereoselective. In all cases, only one reaction product was obtained. Detailed structural analyses of the new polyheterocycles as well as conformational studies including DFT modelling were performed. The relative stability of o-QMs/aza-o-QM were also calculated, and the regioselectivity of the reactions could be explained only when the cycloaddition started from aminodiol 4. It was summarized that starting from diaminonaphthol 25, the regioselectivity of the reaction is driven by the higher nucleophilicity of the amino group compared with the hydroxy group. 12H-benzo[a]xanthen-12-one (11), formed via o-QM formation, was isolated as a side product. The proton NMR spectrum of 11 proved to be very unique from NMR point of view. The reason for the extreme low-field position of proton H-1 could be accounted for by theoretical calculation of structure and spatial magnetic properties of the compound in combination of ring current effects of the aromatic moieties and steric compression within the heavily hindered H(1)-C(1)-C(12b)-C(12a)-C(12)=O structural fragment.
KW  - ortho-quinone methide (o-QMs)
KW  - modified Mannich reaction
KW  - cycloaddition
KW  - NMR spectroscopy
KW  - conformational analysis
KW  - DFT calculations
Y1  - 2019
U6  - https://doi.org/10.1002/open.201900150
SN  - 2191-1363
VL  - 8
IS  - 7
SP  - 961
EP  - 971
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Benzenium Ion
BT  - aromatic as the pi-complex or antiaromatic as the sigma-complex being somewhat similar to the cyclopentadienyl cation
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of the benzenium cation (C6H7+) 1 and of +/- I/M-substituted analogues C6H6X+ 3-8 [X = -Me, -CF3, -NH2, -NO2, -NO, -SiH3] have been calculated using the gauge-independent atomic orbital perturbation method employing the nucleus-independent chemical shift concept, and iso-chemical-shielding surfaces of various sizes and directions have been observed. The TSNMRS values were employed to compare the spatial magnetic properties (TSNMRS) of benzene and the benzenium ion 1 and then further compared with analogues 3-8, to answer the question whether the electronic structures of 1 and 3-8 are still similar to those of aromatic species or somewhat similar to the antiaromatic cyclopentadienyl cation 2, supported by structural data and delta(C-13)/ppm values.
Y1  - 2019
U6  - https://doi.org/10.1021/acs.jpca.9b03121
SN  - 1089-5639
VL  - 123
IS  - 20
SP  - 4443
EP  - 4451
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Stable Carbenes or Betaines?
JF  - European journal of organic chemistry
N2  - The anisotropy effect in H-1 NMR spectroscopy can be readily employed to indicate the position of carbene/betaine mesomeric equilibria. NR2 substituted carbene/betaines tend to adopt betaine structures, whereas in the absence of NR2 substituents, the betaine structures cannot stabilise the structure through both -donation effects of the NMe2 groups and the electronegativity of the nitrogen atoms, and the corresponding carbene-like structures are preferred. These conclusions are supported by calculated bond orders and (C-13)/ppm values. The spatial magnetic properties of isonitriles and carbon monoxide, which can be counted as stable carbenes or, at least, as carbene-analogues, also exist as stable betaine structures, which is again supported by structural and magnetic properties.
KW  - Carbenes
KW  - Betaines
KW  - Mesomerism
KW  - Through-space NMR shieldings (TSNMRS)
KW  - NMR spectroscopy
KW  - Conformation analysis
Y1  - 2018
U6  - https://doi.org/10.1002/ejoc.201800462
SN  - 1434-193X
SN  - 1099-0690
VL  - 2018
IS  - 24
SP  - 3114
EP  - 3121
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Kleinpeter, Erich
A1  - Koch, Andreas
T1  - Quantification of sigma-acceptor and pi-donor stabilization in O, S and Hal analogues of N-heterocyclic carbenes (NHCs) on the magnetic criterion
JF  - The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment & general theory
N2  - The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of stable O, S and Hal analogues of N-heterocyclic carbenes (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 (ICSSs) of various sizes and directions. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the position of the present mesomeric equilibria (carbenes <-> ylides). The results are confirmed by geometry (bond angles and bond lengths), IR spectra, UV spectra, and C-13 chemical shifts of the electron-deficient carbon centers.
Y1  - 2021
U6  - https://doi.org/10.1021/acs.jpca.1c05257
SN  - 1089-5639
SN  - 1520-5215
VL  - 125
IS  - 33
SP  - 7235
EP  - 7245
PB  - American Chemical Society
CY  - Washington
ER  -