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  - 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  - 
TY  - JOUR
A1  - Shainyan, Bagrat A.
A1  - Suslova, Elena N.
A1  - Kleinpeter, Erich
T1  - Conformational analysis of N-phenyl- and N-trifyl-4,4-dimethyl-4-silathiane 1-sulfimides
JF  - Journal of physical organic chemistry
N2  - N-Substituted 4,4-dimethyl-4-silathiane 1-sulfimides Me2Si(sic)S=NSO2R [R- Ph (1), CF3 (2)] were studied experimentally by variable temperature dynamic NMR spectroscopy. Low temperature 13 C NMR spectra of the two compounds revealed the frozen ring inversion process and approximately equal content of the axial and equatorial conformers. Calculations of the 4-silathiane derivatives 1, 2 and the model compound [R Me (3)] as well as their carbon analogs, the similarly N-substituted (sic)S=NSO2R thiane 1-sulfimides [R = Ph (4), CF3 (5), Me (6)] at the DFT/B3LYP/6-311G(d, p) level in the gas phase and in chloroform solution using the PCM model at the same level of theory showed a strong dependence of the relative stability of the conformer on the solvent. The electronegative trifluoromethyl group increases the relative stability of the axial conformer.
KW  - 4-silathianes
KW  - conformational analysis
KW  - dynamic NMR
KW  - quantum chemical calculations
KW  - sulfimides
Y1  - 2011
U6  - https://doi.org/10.1002/poc.1811
SN  - 0894-3230
VL  - 24
IS  - 8
SP  - 698
EP  - 704
PB  - Wiley-Blackwell
CY  - Malden
ER  - 
TY  - JOUR
A1  - Shainyan, Bagrat A.
A1  - Suslova, Elena N.
A1  - Kleinpeter, Erich
T1  - Conformational analysis of 4,4-dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane and 2,2,6,6-tetramethyl-4-(trifluoromethylsulfonyl)-1,4,2,6-oxazadisilinane
JF  - Journal of physical organic chemistry
N2  - 4,4-Dimethyl-1-(trifluoromethylsulfonyl)-1,4-azasilinane 1 and 2,2,6,6-tetramethyl-4-(trifluoromethylsulfonyl)-1,4,2,6-oxazadisilinane 2 were studied by variable temperature dynamic 1H, 13C, 19F NMR spectroscopy and theoretical calculations at the DFT (density functional theory) and MP2 (Moller-Plesset 2) levels of theory. Both kinetic (barriers to ring inversion) and thermodynamic data (frozen conformational equilibria) could be obtained for the two compounds. The computations revealed two minima on the potential energy surface for molecules 1 and 2 corresponding to the rotamers with the CF3SO2 group directed inward and outward the ring, the latter being 0.20.4 kcal/mol (for 1) and 1.1 kcal/mol (for 2) more stable than the former. The vibrational calculations at the DFT and MP2 levels of theory give the values of the free energy difference Delta G degrees for the 'inward' reversible arrow 'outward' equilibrium consistent with those determined from the experimentally measured ratio of the rotamers. The structure of crystalline compound 2 was ascertained by X-ray diffraction analysis.
KW  - conformational analysis
KW  - dynamic NMR
KW  - quantum chemical calculations
KW  - 2
KW  - 6-disilamorpholines
KW  - 4-silapiperidines
Y1  - 2012
U6  - https://doi.org/10.1002/poc.1882
SN  - 0894-3230
VL  - 25
IS  - 1
SP  - 83
EP  - 90
PB  - Wiley-Blackwell
CY  - Hoboken
ER  - 
TY  - JOUR
A1  - Shainyan, Bagrat A.
A1  - Kirpichenko, Svetlana V.
A1  - Kleinpeter, Erich
T1  - Synthesis and conformational properties of 1,3-dimethyl-3-phenyl-1,3-azasilinane low temperature dynamic NMR and computational study
JF  - Arkivoc : free online journal of organic chemistry
N2  - 1,3-Dimethyl-3-phenyl-1,3-azasilinane was synthesized and its conformational behavior was studied by the low temperature NMR spectroscopy and quantum chemical calculations. The compound was shown to exist as an equilibrium mixture of the PhaxMeeq and PheqMeax chair conformers with the N-methyl substituent in equatorial position. The barrier to ring inversion was also determined.
KW  - 1,3-Dimethyl-3-phenyl-1,3-azasilinane
KW  - conformational analysis
KW  - low temperature NMR spectroscopy
KW  - quantum chemical calculations
Y1  - 2012
SN  - 1551-7004
IS  - 24
SP  - 175
EP  - 185
PB  - ARKAT
CY  - Gainesville
ER  -