Self-exchange electron transfer rate constants and reorganization energies for some aromatic compounds in N,N-dimethylformamide determined by elect

Abstract

The rate constants for homogeneous self-exchange electron transfer reactions of nine aromatic and heteroaromatic compounds in N,N-dimethylformamide have been measured by electron spin resonance line-broadening experiments. The aromatic anion radicals were generated electrochemically in a flow cell. The measured rate constants are compared with literature values when possible and self-exchange reorganization energies λ have been calculated. It is found that for all the aromatic and heteroaromatic compounds, except benzophenone, λ 11 ± 1.5 kcal mol −1. For benzophenone a significantly higher value for λ is found (14.7 kcal mol −1. An electrochemical flow cell connected with the cavity of an ESR spectrometer has been used to measure self-exchange ET rate constants and self-exchange reorganization energies for a number of aromatic and heteroaromatic compounds. The obtained values agree with some of the literature values, but with others the differences observed are unsatisfactory and inexplicable. It seems a general problem with such measurements that although accurate measurements (± 10%) can be made in several laboratories, the results obtained in different laboratories may deviate by more than 100%. When comparing reorganization energies for different compounds it seems safest to compare values obtained in the same investigation.