In radical trifluoromethylation the active species is the trifluoromethyl free radical. Reagents such as bromotrifluoromethane and haloform have been used for this purpose but in response to the Montreal Protocol alternatives such as trifluoroiodomethane have been developed as replacement. One particular combination is CFI / triethylborane
Other reagents that generate the CF radical are sodium trifluoromethanesulfinate and bis(trifluoroacetyl) peroxide.
In the CF radical the fluorine atom is an electron-withdrawing group via the inductive effect but also a weak pi donor through interaction of the fluorine lone pair with the radical center's SOMO. Compared to the methyl radical the CF radical is pyramidal (angle 107.8 °C ) with a large inversion barrier, electrophilic and also more reactive. In reaction with styrene it is 440 times more reactive. An early report (1949) describes the photochemical reaction of iodotrifluoromethane with ethylene to 3-iodo-1,1,1-trifluoropropane. Reagents that have been reported for the direct trifluoromethylation of arenes are CFI, CFBr (thermal or photochemical), silver trifluoroacetate/TiO (photochemical) and sodium trifluoromethanesulfinate/Cu(OSOCF)/tBuOOH.