Conformational analysis of 3‐methyl‐3‐silathiane and 3‐fluoro‐3‐methyl‐3‐silathiane |
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| Authors: | Svetlana V Kirpichenko Erich Kleinpeter Igor A Ushakov Bagrat A Shainyan |
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| Institution: | 1. A.E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 1 Favorsky Street, Irkutsk 664033, Russia;2. Department of Chemistry, University of Potsdam, Karl‐Liebknecht‐Str. 24‐25, D‐14476 Potsdam(Golm), Germany |
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| Abstract: | 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 13C 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 (Meax → Meeq) and 5.4 (Meeq → Meax) 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. |
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| Keywords: | conformational analysis low temperature NMR spectroscopy NBO analysis quantum chemical calculations 3‐silathianes |
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