Low-temperature EPR study of the reaction of the 2,2,6,6-tetramethylpiperidyl radical with molecular oxygen. Direct spectroscopic observation of an aminylperoxyl radical

Gamma irradiation of a frozen solution of 2,2,6,6-tetramethylpiperidine in freon-113 at 77 K generates in the first step the piperidine radical cation 1˙+ which deprotonates during annealing at 104 K under formation of the piperidyl radical 1˙. After admission of oxygen at 113 K, the piperidylperoxyl radical 2˙ appears, which is characterized by its EPR powder spectrum (fully anisotropic g-tensor with g1 = 2.0258, g2 = 2.0066 and g3 = 2.0022 at 103 K). Upon warming, 2˙ converts nearly quantitatively to the aminoxyl radical 3˙.