Nuclear magnetic resonance spectra of organogermanium compounds. Part 4. Nuclear magnetic resonance spectra and molecular mechanics calculations of germacyclohexane, methylgermacyclohexanes, and dimethylgermacyclohexanes

Abstract

Molecular mechanics calculations in germacyclohexane and methyl-substituted germacyclohexanes reveals that (i) the ring is flattened around the germanium and that (ii) a methyl group on germanium has a slight preference for the axial conformation rather than the equatorial, which is in line with the results for the corresponding silacyclohexanes. The ¹³C and ⁷³Ge chemical shifts of these germacyclohexanes are consistent with the calculations. Thus, both ¹³C and ⁷³Ge data indicate that 1-methyl-1-germacyclohexane is a ca. 60:40 mixture of axial and equatorial isomers. Attempts to observe directly the two conformers by freezing the inversion on the n.m.r. time scale failed because of the very lower barrier to inversion.