Reductive Cleavage of Carbon Tetrachloride in a Polar Solvent. An Example of a Dissociative Electron Transfer with Significant Attractive Interaction between the Caged Product Fragments

The electrochemical reduction of carbon tetrachloride in N, N ‘-dimethylformamide follows a mechanism in which electron transfer and bond cleavage are concerted, at least at low and moderate driving forces. A detailed analysis of the kinetics of the reductive cleavage reveals that a small but significant interaction between the Cl - and Cl 3 C • fragments exists in the product state and is responsible for a strong acceleration of the reaction. An extension of the theory of dissociative electron transfer is proposed to rationalize the kinetic results and estimate the magnitude of the interaction energy. The model explains how a relatively small interaction energy results in a substantial acceleration of the reaction, caused by both an increase of the driving force and a decrease of the intrinsic barrier. Due to the strong polarization of the CCl 3 radical, the reaction is a particularly clear example of the possibility that attractive interactions between fragments survive in a polar solvent. Another attractive feature of this example is that CCl 4 is small enough a molecule for the application of ab initio techniques, with electron correlation implementation, to be applicable, serving as a complement to the semiempirical model describing the effect of interactions between product fragments on the dynamics of dissociative electron-transfer reactions.