Effects of Bridgehead Substituents on the Stability of the 1-Norbornyl Radical

Abstract

The electrochemical reductive cleavage of a series of 4-X-substituted bicyclo[2.2.1]heptan- 1-yl bromides and iodides (X = H, F, Cl, Br, I, SnMe3) was investigated by means of cyclic voltammetry. By application of the dissociative electron-transfer theory, the variations in the peak reduction potentials translate to values for the weakening of the C-Br and C-I bond dissociation energies (∆D) upon replacement of H by all the substituents (X). The ∆D values suggest significant through-space stabilizing interactions (homohyperconjugation) in the 4-X-substituted bicyclo[2.2.1]heptane radical species.