Kinetics of radical decay. 6. Radical pairs in x-irradiated polycrystalline n-alkoxyazoxybenzenes at low temperature

Abstract

ESR studies indicate that about 70% of the radicals formed by X-radiolysis of poly crystalline samples of n-alkoxyazoxybenzenes at 77 K are produced as closely spaced pairs. Upon warming, the radicals in pairs combine leaving behind a smaller population of chemically different independent radicals. Good correlation between the yield of N2 gas (G(N2) = 0.021) and the yield of radical pairs (G(pairs) ~0.02) in p-azoxyanisole (PAA), as well as spectral differences in deuterated samples and other considerations, indicate the pairs are probably formed by an intramolecular process involving destruction of the azoxy linkage to leave two substituted phenyl radicals separated by a light gas molecule. Overall radical pair decay is "stepwise". Plots of fractional decay vs. time for different doses indicate that pair decay is a correlated process; the method of initial rates gives a reaction order of 0.9 and activation energy 2.7 kcal/mol for recombination in p-azoxyphenetole (PAP); and the pair separation distance is constant during decay, all indicating that the decay occurs by a single jump recombination process involving geminate partners.