Abstract
Abstract The effect of potassium ion-pair formation on the ESR spectra of the anion radicals of 4-nitropyridine and its N-oxide (4NPO) was studied at various temperatures lower than room temperature. The hyperfine splitting constant values due to hydrogen, nitrogen, and potassium nuclei were determined by applying the simulation technique. The above value arising from the potassium nucleus, decreased with a decrease in the temperature. Molecular orbital calculations covering the whole system of the 4NPO−–M+ ion pair and employing the McLachlan modification for the spin-density calculation were carried out in order to discuss the configuration of the ion pairs and the temperature dependence of the hyperfine coupling constants. It was reasonably concluded that an alkali metal cation occupies the C2 axis of the anion radicals and is in contact with the nitro-group oxygen atoms (the symmetry of the ion pairs is C2v.). The temperature dependence of the hyperfine splitting constants was explained using the vibrational model of Atherton and Weissman.
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