Formation and EPR spectra of radical species derived from the oxidation of the spin trap, α-phenyl-N-tert-butylnitrone (PBN), and some of its derivatives in 1,1,1,3,3,3-hexafluoropropan-2-ol. Formation of isoxazolidine radical cations

Abstract

The photolysis of a solution of the spin trap, α-phenyl-N-tert-butylnitrone (PBN, 1) with 2,3-dichloro-4,5-dicyano-1,4-benzoquinone (DDQ) in 1,1,1,3,3,3-hexafluoropropan-2-ol (HFP) containing 6% trifluoroacetic acid produces a persistent radical species, the six-line EPR spectrum of which has a_N = 2.00 and a_H = 2.78 mT. The half-life of this radical was ca. 20 min at 22 °C. A similar spectrum was obtained from PBNs substituted by an electron-withdrawing group (NO₂, F) in the 4-position, whereas PBNs with an electron-donating group (4-MeO, 4-Me₂N, 3,4-OCH₂O) upon oxidation gave multi-line spectra which could be assigned to the corresponding radical cations.