Abstract
-
Cyclopentadienyl derivatives of tin(IV) and mercury(II) and alkylcyclopentadienyl derivatives of mercury(II) are photolysed in solution to show the e.s.r. spectra of the appropriate radicals RC
5 H4 · (R = H, D, Me, Et, Pri, or But). The C5 H5 · radical is a planar π-radical with average D54 symmetry, and its spectrum is broadened in the presence of organic bromides, perhaps by a charge-transfer mechanism. The introduction of alkyl groups breaks the degeneracy of the ψA and ψS molecular orbitals of the π-system by electron release, destabilising the ψS MO, and the e.s.r. spectrum reflects the spin density distribution in the configuration ψA Z ψS 1. Deuterium has a small but detectable perturbing effect : the ψA MO is destabilised by ca. 100 J mol-1, and thermal mixing of the two energy levels results in the configuration ψS 1.515 ψA 1.485. This is compatible with the model of a vibrational perturbation of the resonance integral β, rather than of the Coulomb integral α.