Unstable intermediates

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.