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An electron spin resonance study of nitro-substituted naphthalene anion radicals and ion-pairs Nakano, Fumio


The radical anions and ion-pairs of 1,8-dinitro-naphthalene and 1,4,5,8-tetranitronaphthalene have been perpared and the electron spin resonance spectra have been investigated in detail. The spectra were interpreted completely in terms of a set of two equivalent nitrogen atoms and three sets of two equivalent hydrogen atoms for the 1,8-dinitronaphthalene radical, four equivalent nitrogen atoms and four equivalent hydrogen atoms for the 1,4,5, 8-tetranitronaphthalene radical, respectively. The hyper-fine splitting constants obtained are compared with the values derived from molecular orbital calculations. In the ion-pairs of 1,8-dinitronaphthalene the distinct alkali metal hyperfine splitting have been observed The magnitude of the metal hyperfine splitting shows remarkable temperature dependency, and the temperature dependence is interpreted in terms of the cation exchange mechanism b between two nitro groups of 1,8-dinitronaphthalene. In the anion radical of 1,8-dinitronaphthalene as well as in the corresponding ion-pairs, anormalous line width variation has been observed. This behaviour is interpreted in terms of the cation exchange mechanism and supports the hypothesis proposed for the temperature dependence of alkali metal splitting in the ion-pairs of the compound. In the anion radical of 1,4,5,8-tetranitronaphtha-lene the twisting angle of the nitro group from the plane of aromatic ring is estimated to be (35 ±10)° from the observed splitting constants by employing the spin densities obtained with McLachlan method. The temperature dependency of the nitrogen and hydrogen splittings has been determined. The phenomenon is explained in terms of a hindered rotation of.the nitro group in 1,4,5,8-tetranitronaphthalene. From the asymmetry of the spectra it is predicted that the spin density on the nitrogen nucleus is positive.

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