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 kH/kCl = 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.