Electron Spin Resonance Study of the Self-disproportionation of some Semiquinone Radicals in Solution

The photolysis of 1,4-benzoquinone, duroquinone, and 1,4-naphthoquinone in isopropanol and in dioxane leads to the observation of e.s.r. spectra of the corresponding semiquinone radicals. The rates of the self-disproportionation of these radicals were measured by the rotating-sector technique. In the case of 1,4-naphthoquinone, unexpected e.s.r. emission was initially observed by photochemically induced dynamic electron polarization of the semiquinone radicals. Photolysis of anthraquinone in isopropanol gives e.s.r. spectra of the anthrasemiquinone radical anions. Their rate of decay was measured and a mechanism for the decay was suggested. The neutral anthrasemiquinone radical, however, was observed when photolyzed in dioxane.