Analysis of the Five Unimolecular Reaction Pathways of CDClCHFCl with Emphasis on CDCl(F)C: and CDCl(Cl)C: Formed by 1,1-HCl and 1,1-HF Elimination.

The five unimolecular HX and DX (X = F, Cl) elimination pathways of CDClCHFCl* were examined using a chemical activation technique; the molecules were generated with 92 kcal mol of vibrational energy in a room-temperature bath gas by a combination of CDCl and CHFCl radicals. The total unimolecular rate constant was 9.7 × 10 s, and branching fractions for each channel were 0.52 (2,1-DCl), 0.29 (1,1-HCl), 0.10 (2,1-DF), 0.07 (1,1-HF), and 0.02 (1,2-HCl). Comparison of the individual experimental rate constants to calculated statistical rate constants gave threshold energies for each process as 63, 72, 66, 73, and 70 kcal mol, listed in the same order as the branching fractions. The 1,1-HCl and 1,1-HF reactions gave carbenes, CDCl(F)C: and CDCl(Cl)C:, respectively, as products, which have hydrogen-bonded complexes with HCl or HF in the exit channel of the potential energy surface. These carbenes have energy in excess of the threshold energy for D atom migration to give CDCl═CDF and CDCl═CDCl, and the subsequent cis-trans isomerization rates of the dihaloethenes can provide information about energy disposal by the 1,1-HX elimination reactions. Electronic structure calculations provide information for transition states of CDClCHFCl and hydrogen-bonded complexes of carbenes with HF and HCl. In addition, D atom migration in both free carbenes and in complexes formed by the carbene hydrogen bonding to HCl or HF is explored.