The effects of ion pairing on the EPR spectra of alkyl aromatic hydrocarbon radical anions

Abstract

It is shown that the calculation of spin density changes in radical anions caused by a counterion can be usefully extended to radicals involving hyperconjugation. Such calculations are done for the acenaphthene and pyracene anions and show that the alternating linewidth effects in their EPR spectra are consistent with proposed double potential minima above the aromatic parts of these radicals. New experiments on acenaphthene are reported which support the calculations. The calculation is shown to account successfully for the effects of ion pair formation in 9,10-dihydroanthracene and in benzocyclobutane. Experiments with partially deuterated dihydroanthracene resolve some uncertainty about the assignment of the coupling constants.