1H NMR study of some substituted acyclic silaethanes, 2-silapropanes and 2-methyl-2-silapropanes and their rotameric populations around the Si?C bond

Three series of substituted silaalkanes, (i) SiH₃CH₂X, (ii) MeSiH₂CH₂X and (III) Me₂SiHCH₂X, have been prepared (X=Cl, Br, I, NMe₂, OMe, SMe), and the shifts and coupling constants extracted from their ¹H NMR spectra. Coefficients averaged over three rotameric states can be obtained from the first series which are used for the correction of coupling constants resulting from the presence of the electronegative substituents X. With the aid of the Karplus-Conroy angular dependence of the interproton coupling constants in silaethane? fragments, corrected for electronegative substitution, approximate rotameric populations in series ii and iii were obtained. Except for X=NMe₂, there is always a preference for a synclinal X/CH₃ relationship, even for sandwiched situations (series III).