Line broadening substituent effects

Line-broadening effects are discernible in the epr spectra of many radicals with a- and / -fluorine atom substituents as shown by the results in Table 14. Fluorine atoms at the radical site cause an increase in the barrier to rotation. Line-broadening effects have been observed for the 1,1-difluoroethyl, and 1,1,2,2,2-pentafluoroethyl radicals and other perfluoroalkyl radicals (67,68,94). No line-broadening effects have been detected, however, for the 1-fluoroethyl or the 1,2,2,2-tetrafluoroethyl radicals (68). A detailed analysis of the epr observations for the 1,1-difluoroethyl radical indicates that rotation of the methyl group is apparently responsible for the line broadening rather than the inversion of the carbon atom center (68,94). Meakin and Krusic also concluded that ro-... 

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