Effect of substituted methyl group on the main-chain scission of alkyl radical in solid

ESR measurement of alkyl radicals generated by γ-irradiation of solid polymethylpentanes and polymethylhexanes at 77 K has been carried out to elucidate the effect of substituted methyl group on the scission of alkane main chains. Alkyl radicals initially generated by the scission of the C-H bond are primary radicals, penultimate secondary radicals, or penultimate tertiary radicals if all the penultimate carbon atoms of alkane molecules are tertiary ones. The primary radicals are β-scissile if the β- and γ-carbon are both tertiary. The secondary radicals are stable and not β-scissile. The tertiary radicals are β-scissile if the γ-carbon is tertiary. β-scission does not take place if the γ-carbon is the secondary, since the β-scission induces the conversion of the precursor radicals to unstable primary radicals. A strain introduced into a scissile C-C bond by methyl substitution promoted the β-scission.