Substituent effects in diphenylmercury radical cations: a very clear distinction between σ- and π-states

Abstract

^199/201 Hg ‘satellite’ features have been resolved in electron paramagnetic resonance (EPR) spectra recorded from radical cations of diphenylmercury and its bis-ortho-allyloxy derivatives as isolated in solid freon matrices at 77 K. In accord with our previous work, we confirm that the parent radical cation of diphenylmercury is a σ-species with substantial electron loss from the C–Hg–C bonding region of the molecule: studies of the perdeuteriated analogue reveal a complex superhyperfine structure which persists in CFCl₃ and CCl₄ matrices, and is assigned to coupling from a single matrix chlorine atom.

In marked contrast, the allyloxy derivatives are π-radicals, and show well resolved, nearly isotropic, mercury satellite features that are of the magnitude expected for this assignment. Thus the electron-releasing power of the oxygen atom is sufficient to stabilise the π-state over the σ-state.

The relationship of these results to the mechanism of reactions involving the single-electron oxidation of these organomercurials is discussed.