An electron spin resonance study of the effect of Group IV substituents in cyclopentadienyl radicals

Abstract

E.s.r. spectra have been recorded in solution for the substituted cyclopentadienyl radicals X₃MC₅H₄˙, where X₃M = Me₃Si, Me₂HSi, Me₂ClSi, Me₂FSi, Ph₂ClSi, Cl₃Si, Me₃Ge, Bu₃Ge, Ph₂ClGe, and Me₃Sn. The spectra can be interpreted in terms of perturbation of the orbitals ψ_A and ψ_S which are degenerate in the C₅H₅· radical. This allows the substituents to be placed in the following sequence regarding their electronic interactions, compared with that of hydrogen, with the ψ_S MO of the cyclopentadienyl π-system: electron repelling, Me₃C Bu₃Ge ∼ Me₃Ge > H; electron attracting, H < Me₃Sn < Me₃Si < Me₂HSi < Me₂ClSi < Ph₂ClGe < Me₂FSi < Ph₂ClSi < Cl₃Si.