The Very Weak Visible Absorption Band of p-Benzoquinone

The very weak absorption bands at the long wavelength sides of the n→π* singlet-singlet absorption bands of p-benzoquinone and its derivatives were examined with regard to the solvent effect, the substitution effect and the temperature - dependency. From the obtained results, this absorption band is reasonably assigned to the n→π* singlet-triplet absorption band. As for its absorption curve, a distinct difference between the structure where the two carbonyl groups of p-benzoquinone are equivalent and that where the two carbonyl groups are not equivalent is observed.