The role of internal reorganization in the intramolecular electron exchange of radical anions of disubstituted benzenes

Abstract

The alternating linewidth effects of the e.s.r. spectra of 1,3-dinitrobenzene (3-BDN) and benzene-1,3-dicarbaldehyde (3-BDC) radical anions are interpreted in terms of an intramolecular electron-exchange process with a rate constant of 10⁹ s^–1. For 1,3-dicyanobenzene the absence of linewidth effects suggests a faster electron-exchange process (> 10¹⁰ s^–1). Marcus theory and the intersecting-state model (ISM) are employed to study these electron-transfer processes. Whereas both theories predict the same rate for 3-BDN and 3-BDC, Marcus theory estimates a very low rate (ca. 20 s^–1) for dicyanobenzene radical anions whereas ISM estimates a very fast rate (> 10¹⁰ s^–1) which appears to be in agreement with experiment. The reasons for the difference in the two approaches are discussed.