EPR and ENDOR of perfluoroalkyl radical intermediates in the reaction between perfluorohypofluorites and perfluoroalkenes

Abstract

EPR and ENDOR spectra of the reaction products of sterically hindered perfluoroalkenes with perfluoromethyl hypofluorite and with the perfluoroether hypofluorite X(CF₂O)_n(CF₂CF₂O)_mCF₂OF, where X is either OCF₃ or a second hypofluorite group OCF₂-OF, have been recorded. Tertiary and secondary free radicals are produced by the addition to the alkene double bond of a fluorine atom or of the partner radical formed by the homolysis of the hypofluorite O—F bond. Analysis of the spectra reveals that hyperfine splitting by ¹⁹F nuclei in the γ and δ positions, and even further from the radical centre, contribute spectra. The α- and β-¹⁹F hyperfine splitting are discussed in relation to the radical structure and conformation. The β-¹⁹F splittings are accounted for by the well known equation a^β_F=B cos²(θ); different values of the constant B have to be used according to the number of β-fluorine substituents bonded to the same α-carbon.