Disproportionation‐combination ratios of large branched alkyl radicals

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‐C4H9 and C2H5 with 4,4‐dimethylpentyl‐2, and of iso‐C3H7 with 2,4‐dimethylpentyl‐2 yielded disproportionation‐combination ratios ω for parent‐getter and t‐C4H9‐C2H5 cross reactions, and for the mutual reaction of t‐C4H9 radicals. The unstabilized hot radicals decompose, and these experiments also yielded values for the high‐pressure rate constant ka∞ of 1.70 × 108sec–1 and 2.11 × 107sec–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.