Steven A. Weiner

MEDIUM EFFECTS ON RADICAL-RADICAL REACTIONS

Both esr and flash photolytic methods have been used to follow the bimolecular decay of photochemically generated ketyl radicals. In saturated hydrocarbon solvents, the rates fit a diffusion kinetic model. In benzene and isopropyl alcohol, the rates are slower. There are also rather large substituent effects on reactivity in the “slow” solvents. The substituent effects are not evident in the “fast” solvents. The variation in rate of decay of acetone ketyl radicals in isopropyl alcohol with temperature is perfectly correlated by the temperature dependence of viscosity. We conclude that the rates are in all cases medium-controlled. Whether or not diffusion, in the classical sense, is limiting is a moot question.