title: EPR/spin-trapping study of free radical intermediates in the photolysis of trifluoromethyl ketones with initiators.
abstract: Photolysis of trifluoromethyl ketones (TFMKs) 1a-1e versus the non-fluorinated ketones 2a-2b in the presence of radical initiators by electron paramagnetic resonance spectroscopy has been studied for the first time. The transient radicals generated after irradiation of the ketones were identified by trapping with 2-methyl-2-nitrosopropane (MNP) and 2,4,6-tri-tert-butylnitrosobenzene (TTBNB) as spin traps. TTBNB is a powerful, particularly useful spin trap in these kinds of processes producing anilino and nitroxyl spin adducts due to the ambivalent reactivity on the N and O atoms. In the presence of t-butylperoxide, short-chain TFMKs, such as 1,1,1-trifluoroacetone (1d) and hexafluoroacetone (1e), give rise to detection of the elusive trifluoromethyl radical. In contrast, long-chain TFMKs did not provide clues to prove formation of the trifluoromethyl radical but instead to radicals derived by abstraction of one alpha-methylene proton to the carbonyl. Although TFMKs are quite stable to photodegradation in the absence of initiator, methyl ketone 2b and phenyl ketone 3 produce radicals resulting from abstraction of a gamma-hydrogen to the carbonyl group.
authors.affiliation: Department of Biological Chemistry and Molecular Modellization, IQAC (CSIC), Jordi Girona, 18-26, 08034 Barcelona, Spain.
authors.forename: Esmeralda
authors.initials: E
authors.lastname: Rosa
authors.forename: Angel
authors.initials: A
authors.lastname: Guerrero
authors.forename: Maria Pilar
authors.initials: MP
authors.lastname: Bosch
authors.forename: Luis
authors.initials: L
authors.lastname: Julià
mesh_terms: D004578:Electron Spin Resonance Spectroscopy; D005609:Free Radicals / Q000032:analysis* / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry*; D015394:Molecular Structure; D010782:Photolysis; D012015:Reference Standards
chemical_list: D005609:Free Radicals; D007659:Ketones