Unstable intermediates. Part 138.—The formation of β-bromoalkyl radicals by the action of γ-rays on various organic bromides: electron spin resonance spectra at low temperatures

Abstract

Exposure of ethyl, n-propyl, n-butyl and t-butyl bromide to ⁶⁰Co-γ-rays at 77 K gave, in addition to alkyl radicals, species identified as β-bromo radicals by their e.s.r. spectra. That obtained from t-butyl bromide was the best defined, the radical being Me₂ĊCH₂Br rather than the expected H₂ĊCMe₂Br. This species had a(Me)= 13 G, and A_iso(⁸¹Br)≈ 296 G. Both hyperconjugation and p-p homoconjugation are invoked to explain the results. Similar β-bromo radicals, MeĊH—CH₂Br and H₂Ċ—C(Br)RCO₂H, were formed from allyl bromide and α-bromo acrylic acid.