Electron Spin Resonance of Anion Radicals of Aromatic Esters. III. The Anion Radicals of Several Diesters of Biphenyl-o, o′- and p,p′-Dicarboxylic Acids

Abstract

Abstract The ESR spectra of the anion radicals of dimethyl, diethyl, and diisopropyl esters of biphenyl-o, o′ and -p,p′-dicarboxylic acids, and of the di-t-butyl ester of the o, o′-derivative, have been studied. The anion radicals were prepared by electrolytic reduction in acetonitrile, and also by reduction with sodium and potassium metals in dimethoxyethane and tetrahydrofuran. The MO calculations of the spin densities were made by McLachlan’s method; all the splitting constants observed were assigned to the ring protons and the α-protons in the ester groups. A comparison of the experimental splittings with the calculated spin densities suggests that the anions ofp, p′-derivatives are in a planar conformation, while those of o,o′-derivatives have a twisted structure in which the twisting angle between the two rings was about 35–60°. A structural model was proposed for an ion complex formed between the anion of the o, o′-derivative and a sodium or a potassium cation.