Fluoromethyl radical, stability

The Consequences of Different Stability Definitions How Stable Are Ethyl and Fluoromethyl Radicals ... 

Stabilities of methyl and fluoromethyl radicals have been calculated [114] to be in the order CFj < CHj < CF2H < CFH2 and the relative rates of formation of such radicals, measured in (S-scission reactions of a series of t-butoxy radical derivatives, as shown in Figure 4.45, lend support to this conclusion [115]. 

The irradiation of bis(nonafluoro-tert-butyl)peroxide in octafluorocyclopen-tene or decafluorocyclohexene yields the corresponding vicinal bis(nonafluoro-tert-butyl) diethers in 55 and 63%, respectively [30] Negligible amounts of dimeric or oligomeric products are obtained. Conversely, the similar reaction with bis(tn-fluoromethyl)peroxide yields primarily 2,2 -bis(tnfluoromethoxy)dicycloalkanes (equation 12). The dissimilar behavior is believed to be due to the reduced stability of the trifluoromethyloxy radical and thus its reduced population, which favors oligomerization [30]. 

Experimental support for the given order of stability in the fluoromethyl series has been provided in a study by Jiang et al. of the radical fragmentation of the respective series of fluorinated ferf-butoxy radicals [32] ... 

Several criteria, including hydride affinities of carbocations (R+—H heterolytic BDE) and adiabatic ionization potentials of the corresponding free radicals (Table 1.30), indicate the order of decreasing stability of fluoromethyl carbocations to be CHF2+ > CH2F+ > CF3+ > CH3+ (Scheme 1.54) [1],... 

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