Unimolecular Reactions of CF2ClCFClCH2F and CF2ClCF2CH2Cl: Observation of CIF Interchange

The unimolecular reactions of CF2ClCFClCH2F and CF2ClCF2CH2Cl molecules formed with 87 and 91 kcal mol(-1), respectively, of vibrational energy from the recombination of CF2ClCFCl with CH2F and CF2ClCF2 with CH2Cl at room temperature have been studied by the chemical activation technique. The 2,3- and 1,2-CIF interchange reactions compete with 2,3-CIH and 2,3-FH elimination reactions. The total unimolecular rate constant for CF2ClCF2CH2Cl is 0.54 +/- 0.15 x 10(4) s(-1) with branching fractions for 1,2-CIF interchange of 0.03 and 0.97 for 2,3-FH elimination. The total rate constant for CF2ClCFClCH2F is 1.35 +/- 0.39 x 10(4) s(-1) with branching fractions of 0.20 for 2,3-CIF interchange, 0.71 for 2,3-CIH elimination and 0.09 for 2,3-FH elimination; the products from 1,2-CIF interchange could be observed, but the rate constant was too small to be measured. The D(CH2F-CFClCF2Cl) and D(CH2Cl-CF2CF2Cl) were evaluated by calculations for some isodesmic reactions and isomerization energies of CF3CFClCH2Cl as 84 and 88 kcal mol-1, respectively; these values give the average energies of formed molecules at 298 K as noted above. Density functional theory was used to assign vibrational frequencies and moments of inertia for the molecules and their transition states. These results were combined with statistical unimolecular reaction theory to assign threshold energies from the experimental rate constants for CIF interchange, CIH elimination and FH elimination. These assignments are compared with results from previous chemical activation experiments with CF3CFClCH2Cl, CF3CF2CH3, CF3CFClCH3 and CF2ClCF2CH3.