Free‐Energy Relationship for Mesolytic Cleavage of CC Bonds

What is the functional relationship between the kinetics and thermodynamics for an elementary reaction in solution? This fundamental question was investigated for unimolecular fragmentations of CC bonds in radical ions of bibenzylic substrates such as 1. A Marcus-type free-energy relationship with a parabolic shape fitted the data well. The results imply that mesolytic cleavages have low intrinsic barriers (about 3 kcalmol−1).