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  - 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  -