Unstable intermediates. Part 202. The use of spin traps to study trialkylsilyl and related radicals

Abstract

Exposure of trimethylsilane, containing Me₃CNO molecules in low concentration, to ⁶⁰Co γ-rays at 77 K gave Me₃Si˙ radicals, characterized by their e.s.r. spectra. On annealing, these reacted with Me₃CNO to give Me₃SiN(O)CMe₃radicals (A_N 9.75 G), which have not been reported previously. However, these proved to be short-lived and could not be detected when Me₃Si˙ and related radicals were generated by standard procedures at ambient temperatures. We conclude that Me₃CNO is unsuitable as a trap for such radicals. In contrast, nitrone traps such as PhCHN(O)CMe₃ gave relatively stable radicals with R₃Si˙, the alkyl derivatives being more stable than the aryl derivatives. These radicals were characterized by a relatively large β-proton hyperfine coupling and a coupling to ²⁹Si of ca. 13 G. 2,6-Di-t-butyl-p-benzoquinone also gave relatively stable adducts but these are less readily characterized and we were unable to detect well defined ²⁹Si hyperfine features. The structures of these adducts and the formation of other species are discussed.