Angular dependence of the vicinal interproton spin–spin coupling in silacyclohexanes. The conformational energy term of the methyl group in 1-methyl-1-silacyclohexane

An approximate Karplus-Conroy relationship between the vicinal coupling constants J(H SiCH ) in a silaethane fragment and the corresponding torsional angles τ in silacyclohexanes is proposed. The relationship ³J(H SiCH ) VS τ is asymmetric. The ¹H NMR parameters and conformational features of cis- and trans-3,5-dimethyl-1-silacyclonexane and 3-silabicyclo3.2.1]octane are discussed, and the conformational energy term for the methyl group in 1-methyl-1-silacyclohexane is found to be approximately 1.45 kJ mole^?1 in favour of the axial position for the methyl group, in good agreement with previously calculated values.