Electron spin resonance investigation on cis and trans semidione alkali metal ion pairs

Abstract

The e.s.r. spectra of the ion pairs formed by hexamethoxybibenzoyl semidione with each of the five alkali metals have been recorded in different solvents over the temperature range –80 to +40°C. Two superimposed spectra were observed which are assigned to the ion pairs of the cis and trans isomers of the semidione radical anion, on the basis of g factors, ¹³C splitting and alkali metal splittings. Both cis and trans isomers are found to be associated with the counter ion. The sign of the alkali hyperfine coupling constant is discussed on the basis of linewidth analysis and theoretical calculations of alkali spin densities.