Electron Spin Resonance of Anion Radicals of Aromatic Esters. II. The Anion Radicals of Diesters of o-, m- and p-Phthalic Acids

The ESR spectra have been observed for the anion radicals of several diesters of o-, m- and p-phthalic acids. The radicals were generated by the electrolytic reduction in acetonitrile and also by the reduction with lithium, sodium, potassium and cesium metals in dimethoxyethane (DME) and tetrahydrofuran (THF). The MO calculations of spin densities were made for these radicals by using McLachlan’s method, and the calculated spin densities for the anion radicals of m- and p-phthalates were in good agreement with the experimental splitting constants obtained by electrolysis. In the anion radicals of o-phthalates, the results of calculations taking into account the steric effect between the two ester groups revealed that the twisting angle between each ester group and the ring was 35–45°. From the spectrum of di-t-butyl p-phthalate anion radical prepared by the electrolysis in DME, the t-butyl ester group was found to be in a fixed orientation, probably planar with the ring. It was suggested that an ion complex was formed between the o- or p-phthalate anion radical and each alkali metal cation, and that in the p-phthalatesodium system in DME or THF there existed an equilibrium between an ion complex and a completely dissociated state.