Effect of solid phase on the selectivity of alkyl radical formation by gamma-irradiation of branched alkanes

ESR and electron spin echo measurements of alkyl radicals generated by γ-irradiation of glassy and crystalline branched alkanes C₁₀ ≈ C₁₃ have been carried out to elucidate the effect of molecular structure and solid phase on the selectivity of alkyl radical formation. Alkyl radicals generated and stabilized at 77 K in the glassy alkanes are secondary penultimate radicals. Tertiary radicals and secondary radicals other than the penultimate one are not generated either by hydrogen abstraction or from ionized or exited molecules. In the crystalline alkanes, however, a small amount of secondary internal radicals are generated in addition to the predominant formation of the secondary penultimate radicals. It is concluded that the detachment of C-H hydrogen preferentially takes place at the location where the motion of carbon atoms assisting the detachment of the C-H hydrogen easily occurs.