Formation and reactivity of dimer radical cations of 4-methoxystyrene

One-electron oxidation of 4-methoxystyrene (1) and the following reactions of the radical cations, 1⁺· have been investigated by pulse radiolysis of 1 in 1,2-dichloroethane at room temperature and 77 K matrix γ-irradiation in butyl chloride. Monomer radical cations, 1⁺· with λ_max at 600 nm generated immediately after an 8-ns pulse irradiation react with 1 (k_d = 1.4 × 10⁹ M^-1 s^-1) to form a dimer radical cation with λ_max at 505 nm which was assigned to the head-to-head bonded dimer radical cation (3). The rate constants of the dimer radical cation 3 with 1 (k = 4 × 10⁷ M^-1 s^-1) and with methanol (k_MeOH = 5 × 10⁷ M^-1 s^-1) were measured. On the basis of these results together with those of cyclodimers (2) the effects of a para-methoxyl substituent on the chemical reactivity of 3 are discussed.