Radiolysis of Binary Paraffin—Olefin Solutions. II. Effects of Deuterium Isotopic Substitutions

Abstract

The effects of deuterium isotopic substitutions on product distributions in the radiolysis of paraffin—olefin solutions have been studied. The total hydrogen yield is apparently not affected by deuterium substitution in the olefin. However, the isotopic compositions of hydrogen from mixtures containing deuterated components are typically those expected by hydrogen abstraction involving large isotope effects. Product distributions of dimers from irradiations of cyclohexane—cyclohexene, cyclohexane—cyclohexene-d10, cyclohexane-d12—cyclohexene, cyclohexane-d12—cyclohexene-d10, cyclopentane—cyclohexene, and cyclopentane—cyclohexene-d10 solutions are found to be highly affected by deuterium substitutions in the olefin but scarcely changed by similar substitutions in the paraffin. Such observations are rationalized by the proposal that physical interactions may take place by positive charge transfer from saturated hydrocarbon ions to the olefin, but that the resulting dimer product distributions are governed primarily by subsequent radical scavenging and abstraction reactions. Differences in dimer product yields observed in the various deuterated-vs-nondeuterated mixtures are thus explained by changes in the relative importance of two different reaction sequences each initiated by the olefin positive ion.