Steric effects of nucleophile-radical coupling reaction. Determination of rate constants for the reaction of aryl radicals with 2-naphthoxide anion

Abstract

The absolute rate constants for the reaction of different aryl radicals with 2-naphthoxide anion were determined using an indirect method, a competition of the coupling reaction with the H-atom abstraction. We here show that the radical-ambident nucleophile reactions are sensitive to steric hindrance. A lower reactivity is found for 2-anisyl radical with respect to 4-anisyl and for 2-methoxy-1-naphthyl radical with respect to 1-naphthyl (k_2b < k_2a and k_2d < k_2c). The ortho substitution to the radical centre decreases the rate constant. The reactivity is in agreement with energy barriers determined by theoretical calculations.