Unstable intermediates

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.