Electron transfer induced dissociation of chloro-cyano-benzene radical anion: Driving chemical reactions via charge restraints

We introduce a new quantum mechanics/molecular mechanics based method to drive electron transfer reactions. Our approach uses the dynamically restrained electrostatic potential derived charges of the quantum atoms(1) as a reaction coordinate, and allows an estimation of the free energy barrier of the electron transfer process. Moreover, it provides an accurate description of the electronic structure changes and of the nuclear reorganization associated with the reaction. We use the method to describe the electron-transfer induced dissociation of the m-chloro-cyano-benzene radical anion in aqueous solution. The reaction is triggered by solvent reorganization by a change in the coordination water shell around the cyano nitrogen atom. At the onset of the reaction, charge-spin segregation is observed. The negative charge is transferred to the leaving Cl, while the spin density localizes on the non-saturated carbon atom of the benzene ring. The calculated free energy barrier of dissociation is in good quantitative agreement with the experimental data.