ESR Spectra and Structure of the Fluorinated Methyl Radicals

The ESR spectrum of the CF3 radical has been observed during the irradiation of liquid C2F6. The isotropic fluorine hyperfine splitting in this radical has a value of 144.75 G which is considerably larger than other known values for α fluorine atoms. Well-resolved spectra of CF3·, CHF2·, and CH2F·, as well as certain of the lines of the 13C containing radicals, have also been observed in krypton and xenon matrices. The 13CF3 and 13CHF2 radicals have carbon hyperfine constants of 271.6 and 148.8 G showing that the unpaired electron is in an orbital with considerable s character and that these radicals are therefore non-planar. The carbon and fluorine splittings in CF3· are sufficiently large that third-order correction terms are necessary in considering the line positions. As a result it is demonstrable that the carbon and fluorine hyperfine constants are of the same sign.