Thermodynamics and kinetics of homolytic cleavage of carbon–oxygen bonds in radical anions obtained by electrochemical reduction of alkyl aryl ethers

Abstract

The properties and the reactivity of the radical anions of 4-cyanophenyl alkyl ethers and naphthyl alkyl ethers have been determined by electrochemical methods. Under electrochemical conditions homolytic dissociation is the only observed process. Cyclic voltammetry studies lead to the conclusion that this process is a stepwise one, the initially produced radical anion cleaving by a slow first order reaction followed by a second electron transfer in a DISP1 mechanism. A Marcus type relationship between the cleavage rate constants and the standard free energy of the reaction leads to an intrinsic barrier in the range of 0.7 to 0.8 eV. The analysis of the intrinsic barrier values indicates that solvent organisation represents a modest contribution, the bond dissociation energy of the radical anion (structural contribution) being the main factor in the total barrier. Previously unknown bond dissociation energies of naphthyl ethers have been estimated using the correlations established in this work.