TY  - JOUR
A1  - Shainyan, Bagrat  A.
A1  - Kleinpeter, Erich
A1  - Suslova, E. N.
T1  - Conformational Analysis of (1,1′-Phenyl-1,1′-silacyclohex-1-yl)disiloxane
BT  - DFT and Low-Temperature 13C NMR Spectroscopy Study
JF  - Russian journal of general chemistry
N2  - The DFT and MP2 theoretical conformational analysis of the recently synthesized (1,1-phenyl-1,1-silacyclohex-1-yl)disiloxane has revealed the energetic preference of the Ph-ax,Ph-ax conformer. The Ph-ax,Ph-ax: Ph-ax,Ph-eq: Ph-eq,Ph-eq conformers ratio has been estimated as of 46.6: 33.1: 20.3 from the M062X/6-311G(d,p) free energy simulation, suggesting the possibility of detecting individual conformers experimentally, e.g., by low-temperature H-1 and C-13 NMR spectroscopy. However, only the presence of several conformers has been detected by means of H-1 NMR spectroscopy at 113 K; determination of the (Hz) and G(#) (kcal/mol) parameters for the 6-membered ring interconversion has been impossible due to the signals broadening at low temperature, signal temperature shifts, and extremely low barrier of ring inversion at T-c < 113 K.
KW  - siloxanes
KW  - silacyclohexanes
KW  - conformational analysis
KW  - DFT and MP2 simulation
KW  - low-temperature NMR spectroscopy
Y1  - 2019
U6  - https://doi.org/10.1134/S1070363219040121
SN  - 1070-3632
SN  - 1608-3350
VL  - 89
IS  - 4
SP  - 713
EP  - 716
PB  - Pleiades Publ.
CY  - New York
ER  - 
TY  - JOUR
A1  - Kirpichenko, Svetlana V.
A1  - Kleinpeter, Erich
A1  - Ushakov, Igor A.
A1  - Shainyan, Bagrat A.
T1  - Conformational Analysis of 3-Methyl-3-Silathiane and 3-Fluoro-3-Methyl-3-Silathiane
JF  - Journal of physical organic chemistry
N2  - The conformational equilibria of 3-methyl-3-silathiane 5, 3-fluoro-3-methyl-3-silathiane 6 and 1-fluoro-1-methyl-1- silacyclohexane 7 have been studied using low temperature C-13 NMR spectroscopy and theoretical calculations. The conformer ratio at 103 K was measured to be about 5(ax):5(eq) - 15:85, 6(ax):6(eq)-50:50 and 7(ax):7(eq)-25:75. The equatorial preference of the methyl group in 5 (0.35 kcal mol(-1)) is much less than in 3-methylthiane 9 (1.40 kcal mol(-1)) but somewhat greater than in 1-methyl-1-silacyclohexane 1 (0.23 kcal mol(-1)). Compounds 5-7 have low barriers to ring inversion: 5.65 (ax -> eq) and 6.0 kcal mol(-1) (eq -> ax) (5), 4.6 kcal mol(-1) (6), 5.1 kcal mol(-1) (Me-ax -> Me-eq), and 5.4 kcal mol(-1) (Me-eq -> Me-ax) (7). Steric effects cannot explain the observed conformational preferences, like equal population of the two conformers of 6, or different conformer ratio for 5 and 7. Actually, by employing the NBO analysis, in particular, considering the second order perturbation energies, vicinal stereoelectronic interactions between the Si-X and adjacent C-H, C-S, and C-C bonds proved responsible.
KW  - conformational analysis
KW  - low-temperature NMR spectroscopy
KW  - NBO analysis
KW  - quantum chemical calculations
KW  - 3-silathianes
Y1  - 2011
U6  - https://doi.org/10.1002/poc.1758
SN  - 0894-3230
VL  - 24
IS  - 4
SP  - 320
EP  - 326
PB  - Wiley-Blackwell
CY  - Hoboken
ER  -