Analysis of C–F bond cleavages in methylfluorobenzoates—Fragmentation and dimerization of anion radicals using convolution potential sweep voltammetry

The electrochemical reduction of methylfluorobenzoates at glassy carbon electrodes is analyzed using the convolution potential sweep voltammetry (CPSV). The stabilization of the radical anion due to the electron-withdrawing group is shown to lead to intra-molecular stepwise dissociative electron transfer. While methyl 2-fluorobenzoate (ortho isomer) follows EC mechanism, the methyl 4-fluorobenzoate (para-isomer) undergoes electro-dimerization prior to C–F bond cleavage. The first order rate constant for the EC mechanism and the dimerization rate constant for the electro-dimerization are deduced from the classical as well as convolution potential sweep voltammetry. A plausible mechanism of dimerization is suggested. The influence of the electron-withdrawing groups is illustrated by comparing the reduction behaviour of 4-fluorobenzonitrile. The potential energy surfaces and electron density mapping employing Gaussian 03 calculations provide further support for the validation of the mechanism pertaining to C–F bond cleavages.