Structure, Properties, and Reactivity of Perfluoroalkyl Radicals

Thermodynamically, perfluoroalky] radicals are not generally more stable or they are even more destabilized than alkyl radicals. Nevertheless, several factors can dramatically stabilize perfluoroalky] radicals kinetically. 

The structure and reactivity of perfluoroalkyl radicals is determined by the complex interplay between the strong (7-acceptor effect and the w-donating effect of fluorine. Whereas the methyl radical is planar, fluorinated methyl radicals are pyramidal [9]. The pyramidalization and inversion barriers increase with increasing fluorination [10]. The calculated inversion barriers are 1, 7, and 25 kcal mol for CHjF, CHFj-, and CF,-, respectively [11]. 

The reactivity of perfluoroalkyl radicals can be summarized again under the motto Think Negative . As a kind of starting point, the absolute electronegativities (as a measure of reactivity) [12] of the methyl and trifluoromethyl radicals 

---