Unstable intermediates. Part 113.—E.S.R. data for R2ĊXR3 radicals, when X is from group IV or V. Evidence against significant d(π)—p(π) bonding

Abstract

A wide range of R₂ĊXR₃ radicals has been prepared, generally in the solid-state, by γ-irradiation of the corresponding alkyl derivatives such as R₄Sn, R₄Pb, R₄P⁺ hal^– and R₄As⁺ hal^–. From the magnitudes of the hyperfine coupling to α-protons, methyl protons, and X nuclei, it is concluded that for all these radicals, delocalization onto X is undetectably small, and therefore < ∼1 %.

Arguments in favour of π-bonding, previously adduced from trends in the g-values for radicals containing Group IV elements, are shown to be unconvincing, since for Group V elements the trend is reversed.