Title compound, a cross-conjugated biradical with phenoxylnitronyl nitroxide structure, was prepared by the lead dioxide oxidation of a p-hydroxyphenyl nitronyl nitroxide, 2-(3,5-di-tert-butyl-4-hydroxyphenyl)-4,4,5,5-tetramethyl-4,5, -dihydro-1H-imidazole-3-oxide-1-oxyl (1b), and was characterized by ESR spectroscopy. On the other hand, the gamma-radiolysis in a freon matrix and the anodic or chemical oxidation of Ib did not generate 2b but lead to the formation of a phenol-substituted nitronyl nitroxide cation 3b. Thus, a stable acid/base pair with different spin multiplicities, 2b and 3b, could be prepared independently.