Free radical substitution in aliphatic compounds. Part 33. Halogen atom abstraction from alkyl halides by trimethylgermanium radicals in the gas phase

Abstract

Mixtures of trimethylgermanium hydride and halogenoalkanes have been irradiated by a medium pressure mercury lamp. A rapid reaction has been observed in which a halogen atom on the original halogenoalkane is displaced by a hydrogen atom and trimethylgermanium halide is formed. The reaction is exactly similar to that previously reported for trimethyltin hydride, and is interpreted as a radical chain reaction. The reactivity of different sites in monosubstituted alkanes is in the order tertiary > secondary > primary but trimethylgermanium radicals are less selective than trimethyltin radicals. However, in chlorine abstraction from a range of compounds with the general formula RCCl₃, trimethylgermanium radicals are considerably more selective. These apparently conflicting results are interpreted in terms of polar forces in the transition state.