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 (AN 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.