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Conformational analysis of 3‐methyl‐3‐silathiane and 3‐fluoro‐3‐methyl‐3‐silathiane
Author(s) -
Kirpichenko Svetlana V.,
Kleinpeter Erich,
Ushakov Igor A.,
Shainyan Bagrat A.
Publication year - 2011
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/poc.1758
Subject(s) - conformational isomerism , chemistry , steric effects , vicinal , natural bond orbital , ring flip , nuclear magnetic resonance spectroscopy , stereochemistry , methyl group , crystallography , ring (chemistry) , computational chemistry , molecule , group (periodic table) , density functional theory , organic chemistry
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 13 C 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 (eq → ax) kcal mol −1 ( 5 ), 4.6 ( 6 ), 5.1 (Me ax → Me eq ) and 5.4 (Me eq → Me ax ) kcal mol −1 ( 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. Copyright © 2010 John Wiley & Sons, Ltd.