Perfluoroethyl radicals

The absolute Arrhenius parameters for the H-abstraction reactions of perfluoroethyl radicals shown in Table 27 have been calculated by assuming A = 4 x 10 1 mole sec and E = 0 kcal mole for the 

Metathetical reactions of perfluoroethyl radicals transfer of hydrogen atoms 

Metathetical reactions of perfluoro-n-propyl radicals transfer of hydrogen atoms n-C3F7 + RH n-CsF H + R 

The Arrhenius parameters refer to attack on the total molecule and are not expressed per H atom available the data are based on log(fe/l mole sec ) = 8.6 for the combination of n-C3F7 radicals. 

Much of the data in Table 27 have been obtained using perfluorodiethyl ketone as the radical source. More recently, Chamberlain and Whittle [331] have shown that the photolysis (X — 2540 A) of perfluoropropionic anhydride is an excellent clean source of C2 F5 radicals. 

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IR absorptions of these species were assigned to fundamental modes by comparison with the spectra of stable perfluoroorganic compounds. Normal coordinate analysis of the perfluoroethyl radical was performed and the valence force field of C2F5 was calculated (Snelson et al., 1981). 

By contrast, perf luoro/ir-f luoro effect reasoning correctly suggests B-fluorination of ethyl radical will increase the ionization potential because the species is nonplanar. For perfluoroethyl radical, the two fluorination effects on ionization potentials run counter to each other. Experiment does not help us decide which effect dominates because the heat of formation of C2F5+ is known no better than 15 kcal mol"1. That is, from appearance potentials of this ion from C2F5Z with Z = F, I, CF3 and C2F5 we obtain ionization potentials of 228, 218, 208 and 199 kcal mol"1 (ca. 9.88, 9.45, 9.02 and 8 63 eV). This is clearly too wide of a spread of values to be of thermochemical use to derive meaningful substituent effects. 

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