Selectivity of Alkyl Radical Formation from Branched Alkanes Studied by Electron Spin Resonance and Electron Spin Echo Spectroscopy

Article abstract of DOI:10.1021/j100198a032

Electron spin resonance and electron spin echo measurements of alkyl radicals generated from branched alkanes by γ-irradiation have been carried out to elucidate the mechanism of selective alkyl radical formation in low-temperature solids.Alkyl radicals generated at 77 K are primary and penultimate secondary radicals.The primary radicals are generated from alkane radical cations and excited alkanes.Hydrogen atoms and the primary radicals selectively abstract hydrogen atoms on the penultimate secondary carbon atoms of nearby alkanes.Primary C-H hydrogen atoms are not abstracted because of their high activation energy.Tertiary radicals and secondary radicals other than the penultimate one are not generated either by hydrogen abstraction or from excited or ionized molecules, since the motion of carbon atoms assisting the detachment of a C-H hydrogen atom is impeded by alkyl chains attached to the C-H carbon atom.In contrast to the reaction in the glassy solids, the selectively of radical formation in liquids simply follows the order of C-H bond dissociation energy.