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The effects of impurities on the ESR of DPPH in various solutions were studied. The broad quintet spectrum usually obtained with DPPH solutions becomes well resolved after dissolved gases are removed. Addition of tertiary hydroperoxides to DPPH solutions gives a triplet spectrum, which further splits into 17 lines after subsequent degassing in the case of t-butyl hydroperoxide. From an analysis of this spectrum, a determination was made of the spin-density distribution of the unpaired electron in a species electronically analogous to biphenylaminium ion. An aerated DPPH solution of xylene loses its paramagnetic nature in time, but regeneration of the quintet ESR spectrum of DPPH is observed if this solution is mixed with the so-called lophine-x compound solution kept in the dark, and then irradiated by sunlight. The interpretation of this phenomenon is that the lophine-x compound, when irradiated by sunlight, has an odd electron which shifts onto the nonparamagnetic DPPH—O2 reaction product regenerating DPPH as a result. This is, therefore, a radical transfer reaction and is one of the few chemical reactions giving evidence for the radical nature of the lopine-x compound when photochemically excited.

A series of monocarboxylic acids and esters have been γ-irradiated at 77°K, either pure or in the rigid matrix of 2-methyltetrahydrofuran, and the products have been examined by ESR spectroscopy. The spectra obtained in the pure state showed that the primary paramagnetic species in each case is the corresponding radical anion, (Remark: Graphics omitted.). In the rigid matrix, these characteristic spectra have been obtained after illuminating the γ-irradiated sample with visible light at the expense of the spectra of trapped electrons. When ultraviolet light was used for the illumination, the spectra of the radical anions disappeared, but instead appeared the spectra of the radicals produced by the decomposition of the radical anions. The latter spectra were almost the same as those obtained by the direct photolyses of acids and esters.

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