pp Homoconjugation in organic radicals

ESR data for various radicals of type R₂?CR₂X, when R is H or alkyl, and X is either Cl, Br or I, or PR₂ and AsR₂, are discussed in terms of pp homoconjugation. For the β-halogen radicals, the small size of the anisotropic coupling provides some evidence for this effect, but for the β-PR₂ and β-AsR₂ radicals, the greatly enhanced isotropic coupling to ³¹P or ⁷⁵As compared with those for the corresponding cation-radicals, R₂?CR₂PR⁺₃ or R₂?CR₂AsR⁺₃, is taken as good evidence for homoconjugation.