ESR studies of free radicals derived from hydroxyquinones. Naphthazarin revisited: twentyfive years of alternating linewidth effect

The neutral semiquinone radical obtained by photolysis of naphthazarin in THF exhibits linewidth alternation. The temperature dependence of the ESR spectrum has been interpreted in terms of a restricted rotation of the hydroxyl groups with and activation energy of 22.7 kJ/mol.