An electron spin resonance study of the methylcyclopentadienyl radicals, MenH5 –nC5·(n= 1–5)

Abstract

The radicals Me_n C₅H_{5 –n}· have been generated by photolysis of the corresponding hydrocarbons (n= 3–5) or mercury derivatives (n= 0–5) and their e.s.r. spectra have been recorded. The spectra are interpreted in terms of thermal population of the ψ_A and ψ_S molecular orbitals, for which the predicted hyperfine coupling constants are calculated by the McLachlan equation, taking λ 0.75 and Q(C₅H₅·)–30 and Q(Me₅C₅·) 31.85 G. The energy separations between the ψ_A and ψ_S MOs can be rationalised on the assumption that a methyl substituent on a carbon atom of the cyclopentadienyl carrying a unit π-electron has a destablising interaction, within a factor of two, of 10 kJ mol^–1.