ELECTRON SPIN RESONANCE STUDIES ON ION PAIR ASSOCIATION AND 13C HYPERFINE SPLITTINGS IN POTASSIUM P-BENZOSEMIQUINONE

Esr studies on the temperature dependence of the proton and 13C hyperfine splittings in p-benzosemi-quinone anion produced by alkali metal reduction have been carried out in detail. Tight or contact ion pairs and unassociated radical ions have been found to exist simultaneously in samples of p-benzosemiquinone-K+ in 1,2-dimethoxyethane at low temperatures. The proton and 13C splittings from unassociated and tight ion pairs were measured and the spin densities in the two types of radical species were evaluated using the experimental data. MO calculations were performed to fit the spin densities at all the positions in a given radical species. The spin density redistribution that takes place as a consequence to the formation of a tight ion pair has been discussed in the light of the MO results. There is also evidence from a study of the 13C splittings that there is an intramolecular migration of the counterion in the tight ion pair at higher temperatures. The tight ion pairs have lower g values compared to the unassociated radical species. © 1968, American Chemical Society. All rights reserved.