An ESR study of aromatic olefin radical cations.

γ-Irradiation of phenyl- and diphenylethenes in CFCl3 matrix at 77 K resulted in the formation of the substrate radical cations. 1,1-Diphenyl-2-methylpropene radical cations exhibit a spin density (ρ=0.45) at the β carbon much higher than those of stilbene and 2-styrylnaphthalene radical cations and comparable to those of styrene and α-methylstyrene radical cations. The spin density at the vinyl carbons appears to play an important role in governing the reactivity of the olefin radical cations with molecular oxygen.