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Development of fluorinated, NMR-active spin traps for studies of free radical chemistry

1989; Elsevier BV; Volume: 81; Issue: 1 Linguagem: Inglês

10.1016/0022-2364(89)90266-7

1557-8968

Barry S. Selinsky, Louis Lévy, Ann G. Motten, Robert E. London,

Free Radicals and Antioxidants

Five fluorinated analogs of the spin trap phenyl-t-butyl nitrone (PBN) have been synthesized and evaluated for use as NMR-active traps. The introduction of the fluorine substituent allows selective observation of chemical reactions involving the spin traps. Although the paramagnetic adducts themselves are not directly observable by this approach as a consequence of extensive broadening, the reduced forms (hydroxylamines) can be readily observed. NMR studies of the trapping of the phenyl radical produced from the thermal decomposition of phenylazotriphenyl methane have been carried out. The observation of fluorinated benzaldehydes in these studies reflects the formation and subsequent degradation of oxygen-centered radicals under some conditions. Relative trapping efficiencies for the phenyl radical in the series 2-F, 4-F, 2,6-difluoro, 2-CF3, and 4-CF3 substituted PBN analogs have been determined based on an analysis of the 19F NMR resonance intensities of the reduced phenyl radical adducts. The relatively large proton hyperfine coupling constants observed for 2,6-difluoro and 2-CF3 PBN analogs allow direct observation by ESR of adduct formation in solutions containing both PBN and either of these analogs. The introduction of fluorine substituents into the trap has only a small effect on trapping efficiency.