Disproportionation-Recombination Rate Ratios for Hydroaromatic Radicals

Article abstract of DOI:10.1021/j150668a033

Relative rates for radical disproportionation (R^. + R'^. <*> RH + R'_d) and recombination (R^. + R'^. <*> RR') have been determined in the liquid phase at 150 deg C for a series of reactions involving resonance-stabilized hydroaromatic radicals.Self-reactions were studied for the 1-tetralyl, 1-indanyl, 9,10-dihydro-9-phenanthryl, and 9,10-dihydro-9-anthryl radicals.Four cross-radical reactions involving benzyl, diphenylmethyl, and 1-tetralyl radical as H-atom acceptors were also examined.Rate constant ratios (k_d/k_r) span the range of 1.34 for the self-reaction of 9,10- dihydro-9-phenanthryl radicals to 0.05 for the self-reaction of 9,10-dihydro-9-anthryl radicals.When disproportionation reaction exothermicity is sufficiently small, -ΔH_d -1 (210 kJ mol^-1), disproportionation rate constants decrease with decreasing exothermicity.A fit of liquid-phase data yields ln (k_d/k_r) per H atom = -10.1 - 0.163 ΔH_d (kcal mol^-1).