Absorption spectra of dimer cations. Part 2.—Benzene derivatives

Abstract

Radical cations of benzene, fluorobenzene, toluene, m-xylene, mesitylene, hexamethyl-benzene and p-tert-butyl-toluene have been prepared by γ-radiolysis of glassy solutions in a mixture of isopentane and n-butyl chloride at 77 K. The effects of concentration and of slight warming are used to assign the absorption bands to monomeric and dimeric species (M⁺ and M⁺₂); the latter presumably have “sandwich” configurations like excimers. The assignments are supported by the resemblance of the dimer bands to those of para-cyclophane : some α,ω-diphenyl alkanes were also studied. Attempts at preparing “dimer anions” were unsuccessful, except with para-cyclophane. The spectra of the cations of the methyl-benzenes showed extra peaks, probably due to carbonium ions formed by hydrogen-atom transfer.