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  - 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  - 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  - 
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  -