Rate constants for the reaction of tert-butyl radicals with chloroform in solution

The decay of photochemically generated tert-butyl radicals in methylcyclopentane solutions containing chloroform is studied by time-resolved ESR spectroscopy. In the pure solvent it perfectly follows the second-order rate law for radical self-termination. Increasing chloroform concentrations cause increasing admixture of a pseudo-first-order decay from which the rate constant of the title reaction is obtained. For 273 K ≦ T ≦ 323 K, where θ = 2.303RT kcal/mol. CIDNP studies of the reaction mechanism and NMR product yields show H and Cl abstractions to occur with the temperature-independent ratio k_H/k_Cl = 1.4 ± 0.1. The results point to polar effects in the transfer reactions of tert-butyl. The potential of time-resolved ESR spectroscopy in studies of first- and pseudo-first-order reaction rates is discussed.