Solvent effect on kinetics of the chloride ion cleavage from anion radicals of 4-chlorobenzophenone

Abstract

Formal potentials (expressed on the ferrocene scale) for the formation of 4-chlorobenzophenone anion radicals ERX/RX−o as well as for the Cl/Cl− couple increase with the solvent acceptor number but the second dependence is at least twice as strong. However, the rate constant for CCl bond cleavage in these radicals decreases with solvent acidity, indicating that solvation of the leaving anion does not determine the kinetics of cleavage. It is shown that solvent effects on the intrinsic rate constant are dominant and can be described by the Pekar factor, as proposed in the Savéant model.