Abstract
Recently, Hollocher and Weber published electron spin resonance spectra of alkaline aqueous systems containing partially reduced 2-hydroxy-3-methyl-1,4-naphthoquinone (I), but did not identify the radical responsible. We now give evidence that the semiquinone of (I) is responsible for the observed spectra. Comparisons among the spectra obtained with the foregoing system and with similar systems containing other 2-hydroxy-1,4-naphtho- quinones indicate that the apparent complexity of the hyperfine structure arises from a non-equivalence of the four benzenoid ring protons to give three different splittings with consequent overlapping of individual lines.