Chemistry of Nuclear Recoil 18F Atoms. IV. Hot F-to-HF and F-to-F2 Abstraction in CH3CF3

Abstract

New hot abstraction reaction channels have been demonstrated for nuclear recoil 18F atoms reacting with fluorocarbon substrates. Hot F-to-HF abstraction in CH3CF3 is a very efficient process with an absolute hot yield of 51%±3%. Hot F-to-F2 reactions also occur, but with much lower efficiencies. The F-to-F2 absolute hot yields in CH3CF3, C2F6, and C3F6 are 5.4%±0.3%, 6.9%±0.8%, and 11.7%±0.5%, respectively. In good agreement with theoretical expectations, translational excitation appears to be much more effective as a driving force for the exoergic F-to-HF process in comparison with the endoergic F-to-F2 process. The Arrhenius activation energy for thermal F-to-HF abstraction in CH3CF3 is at least 2.1±0.1 kcal/mole larger than the value associated with the thermal 18F-atom pi-addition process in C3F6.