Hydrogenations of (4-methylphenyl)trimethylsilane, [4-(trifluoromethyl)phenyl]trimethylsilane, and 1,4-bis(trimethylsilyl)benzene provide the corresponding predominantly cis (∼80%) 4-substituted cyclohexyltrimethylsilanes on the basis of H, C, and F nuclear magnetic resonance spectra. These spectra, and in particular the low-temperature F spectra of cis-[4-(trifluoromethyl)cyclohexyl]trimethylsilane, require the conclusion that the conformational A value for the trimethylsilyl group is essentially the same as that of trifluoromethyl, viz., 2.4–2.6 kcal/mol.
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Kitching et al. (1982) studied this question.