Triplet-state electron spin resonance studies of aryl cations. Part 4.—Low-temperature kinetics of the decay of 3Ar+ in crystalline and glassy media

Abstract

The rates and kinetics of decay of triplet-state aryl cations (3Ar+) in the temperature range 82–120 K are highly dependent on both the substituent groups and the nature of the environment. Amino-substituted 3Ar+ decays by second-order kinetics far more rapidly in microcrystalline samples at all temperatures than RO- or RS-substituted analogues, although the activation energies all fall in the range 22.1 ± 1.7 kJ mol–1. In LiCl—H2O glasses, 2,5-di-n-butoxy-4-morpholinophenyl cation decays at temperatures below the matrix T0 value according to the Dole ‘Q-function’, which corresponds to two parallel second-order processes taking place in different reaction zones (probably without diffusion between zones): these decays also exhibit ‘stepwise’ behaviour if the temperature is raised during the very slow final section of the decay at a given temperature. At least part of the decay of 3Ar+ results in formation of the species Ar˙.