Unstable intermediates. Part 122.—Electron spin resonance studies of radicals from irradiated trimethylphosphine oxide: the Me2PO radical

Abstract

Exposure of trimethylphosphine oxide to γ-rays at 77 K gave, after slight annealing, e.s.r. spectra with separate features assigned to Me₃PO^–(or Me₃POR), Me₂PO and H₂ĊPO(Me)₂ radicals. At ca. 140 K the spectrum assigned to Me₃PO^– radicals was lost irreversibly, whilst that assigned to Me₂PO radicals changed reversibly to reveal well resolved proton hyperfine structure, with a(H)= 5.6 G. This temperature effect is explained in terms of extensive librations of the radicals, coupled with concerted restricted rotation of the methyl groups.

In alcohol media, only Me₃PO or Me₃POH radicals were detected, whilst in sulphuric acid the main phosphorus radicals were Me₃P⁺ and H₂Ċ—P(OH)Me⁺₂.