Linewidth Effects in the ESR Spectra of 2,2′-Dinitrodiphenyl Radical Anion Obtained by Alkali Metal Reduction

Abstract

The ESR spectra of anion radicals, obtained by reduction of 2,2′dinitrodiphenyl with lithium, sodium, and potassium in dimethoxyethane (DME) and tetrahydrofuran (THF), in the temperature range +50°– − 80°C, are discussed. The two nitrogen couplings are not equivalent in the anion radical obtained by lithium reduction, while they are equal in the case of sodium and potassium reduction in both DME and THF. Anomalous linewidth behavior is observed in all these spectra which depend on temperature and solvent, as well as the cation. Freed and Fraenkel's relaxation-matrix theory is used to explain the observed linewidth behavior, taking into account the metal-ion exchange between the two nitro groups. Such pronounced variation in linewidth, which has not been hitherto reported in the metal reduction of dinitro compounds, is attributed to the favorable spatial disposition of the nitro groups in 2,2′-dinitrodiphenyl.