Absolute rates for dimerization of capto-dative substituted methyl radicals in solution: absence of kinetic stabilization

Abstract

For three capto-dative substituted methyl radicals, t-butoxy(cyano)methyl radical (1), t-butylthio(cyano)methyl radical (2), and methoxy(methoxycarbonyl)methyl radical (3), absolute rates for dimerization have been measured by e.s.r. spectroscopy and substantiated by product analysis. Values for the rate constants of 1.0 × 10⁸–1.5 × 10⁹ I mol^–1 s^–1 in the temperature range –60 to +60 °C support the diffusion-controlled nature of the dimerization. The comparison of Arrhenius activation parameters for dimerization with those for the bulk viscosity of the solutions does not provide evidence for noticeable intrinsic barriers to recombination, indicating the absence of kinetic stabilization for capto-dative substituted methyl radicals.