New Benzo-15-Crown-5 based nitronyl-nitroxide and the corresponding imino-nitroxide radicals have been synthesized and characterized. 4 ' -Formyl-benzo-15-crown-5 reacts with N,N ' -dihydroxy-2,3-diamino-2,3-dimethylbutane to yield the N,N ' -dihydroxyimidazolidine and the dehydration product N-hydroxyimidazolidine. Mild oxidation of these two species leads to the corresponding stable nitronyl-nitroxide and imino-nitroxide radicals respectively.