Disproportionation‐combination ratios of large branched alkyl radicals

Abstract

Abstract The disproportionation‐combination reactions of radicals 4,4‐dimethylpentyl‐2 and 2,4‐dimethylpentyl‐2, produced by collisional stabilization of the respective chemically activated species, have been studied at 298°K, with and without getter radicals. Use of getters t ‐C 4 H 9 and C 2 H 5 with 4,4‐dimethylpentyl‐2, and of iso‐C 3 H 7 with 2,4‐dimethylpentyl‐2 yielded disproportionation‐combination ratios ω for parent‐getter and t ‐C 4 H 9 ‐C 2 H 5 cross reactions, and for the mutual reaction of t ‐C 4 H 9 radicals. The unstabilized hot radicals decompose, and these experiments also yielded values for the high‐pressure rate constant k a ∞ of 1.70 × 10 8 sec –1 and 2.11 × 10 7 sec –1 for 4,4‐dimethylpentyl‐2 and 2,4‐dimethylpentyl‐2, respectively. The results, compared to those for other large alkyl radical systems obtained earlier, suggest that steric effects influence the accessibility of H atoms for transfer.