Reinvestigation of the Unimolecular Reactions of CHF2CHF2: Identification of the 1,1-HF Elimination Component from Addition of :CFCHF2 to trans-2-Butene

The recombination of ·CHF2 radicals in a room-temperature bath gas was used to generate CHF2CHF2* (where * indicates vibrational excitation) molecules with 96 kcal mol–1 of vibrational energy. The CHF2CHF2* molecules decompose by four-centered 1,2-HF elimination and by three-centered 1,1-HF elimination reactions to give HF and either CHF═CF2 or :CFCHF2, respectively. The 1,1-HF component was identified by trapping the :CFCHF2 carbene with trans-2-butene that forms 1-fluoro-1-difluoromethyl-2,3-dimethylcyclopropane. The total rate constant for the decomposition of CHF2CHF2* was 6.0 × 105 s–1, and the rate constant for the 1,1-HF pathway forming the carbene, as measured by the 1-fluoro-1-difluoromethyl-2,3-dimethylcyclopropane yield, was 1.4 × 105 s–1. On the basis of matching the experimental rate constants to calculated statistical rate constants, the threshold energies for the four-centered and three-centered reactions are 78 and ≤85 kcal mol–1, respectively.