A NEW AND RIGOROUS METHOD FOR CALCULATING INTRAMOLECULAR REORGANIZATION ENERGIES FOR ELECTRON-TRANSFER REACTIONS - APPLIED FOR SELF-EXCHANGE REACTIONS INVOLVING ALKYL AND BENZYL RADICALS

A new method has been developed for obtaining the reorganization energy for the changes in the intramolecular degrees of freedom during an electron-transfer reaction. This method is based on the use of analytic gradient and Hessian formalism and is an improvement over previous efforts to obtain the intramolecular reorganization energy for larger organic molecules. This approach is expected to be useful, and a preliminary application is presented. The differences in reorganization energies measured for alkyl and benzyl radicals arc discussed. Experimental investigations have shown the existence of significant differences in reorganization energies for self-exchange reactions of aliphatic (50 +/- 10 kcal mol-1) and benzylic (15 +/- 5 kcal mol-1) radicals. Most puzzling is why these large differences appear for self-exchange reactions of alkyl anions/radicals and benzyl anion/radicals. The focus is on current experimental reactions of interest: self-exchange reaction with (i) benzyl anion and benzyl radical and (ii) butyl anion and butyl radical, as donor and acceptor. The difference in reorganization energy is investigated in terms of the conventional Marcus theory dividing the reorganization energy into two separate contributions, the solvent reorganization and the intramolecular reorganization.