Electron spin resonance study of the radical anion of p-bis(pentamethylbenzoyl)benzene

Abstract

The e.s.r. spectra of the radical anion of p-bis(pentamethylbenzoyl)benzene are superpositions of those of the two isomers. For the free anion, obtained by electrolytic reduction in dimethylformamide or potassium reduction in hexamethylphosphoramide, the trans/cis ratio is dependent on solvent but independent of temperature. At low temperatures the spectra obtained from potassium reduction in ether solvents are characteristic of locked unsymmetrical ion pairs. Linewidth alternation owing to intramolecular cation exchange occurs at higher temperatures and the rate of this process has been measured. The trans/cis ratio and the proton hyperfine coupling constants are temperature dependent in the ion pairs and have also been characterised. Qualitative results for ion pairs with lithium, sodium and caesium are reported.