The influence of crown ethers on cation migration processes. Part 4. Some simple benzoquinone radical anions in the presence of dibenzo-18-crown-6

Abstract

The radical anions of 2,5-di-t-butyl- and 2,5-dimethyl-benzoquinone have been prepared in 1,2-dimethoxyethane with Li⁺, Na⁺, or K⁺ as the counterion in the presence of dibenzo-18-crown-6. Linewidth alternation is observed in the e.s.r. spectra of these radical anions, with the lifetime of the counterion at one of the preferred sites near the radical anion varying in the sequence Li⁺ > Na⁺ > K⁺ at a particular temperature. It is apparent that in the presence of the crown ether ‘contact’ ion pairs are still present in the majority of the systems studied. The relatively minor influence of the crown ether on these systems is probably a result of the similarity in cation solvation environment presented by 1,2-dimethoxyethane and the crown ether.