Conformational behavior of 3,3-dimethyl-3-silathiane 1-oxide and its diastereomeric 2-methyl derivatives

The conformational behavior of 3,3-dimethyl-3-silathiane 1-oxide 3 and its trans-4 and cis-4 2-methyl derivatives has been studied by 1H and 13C NMR. The equatorial conformer 3-eq for 3 and the diequatorial isomer trans-4-eq for trans-4 predominate (>95%) in CDCl3 solution. In contrast, the cis-4-ax conformer is the more preferred form of cis-4. The conformational free energy (ΔG°) in the equilibrium cis-4-ax ↔ cis-4-eq was determined to be about +0.01 and +0.52 kcal mol−1 at 26 and −120°C, respectively. The Gibbs free energy of activation (ΔG ‡) for the inversion cis-4-ax → cis-4-eq was estimated to be 8.1 kcal mol−1 at −100°C.