Electron-Spin-Resonance Studies of DPPH Solutions

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.