Theoretical Study of the Thermal Decomposition Pathways of 2-H Heptafluoropropane

The structures, vibrational frequencies, and energetics of 2-H heptafluoropropane (CF₃CHFCF₃) as well as the thermal decomposition products and transition-state molecules have been studied theoretically with both ab initio and density functional methods. Of a total of 12 primary reaction pathways, two have been identified as thermodynamically and kinetically favorable reactions. These are (1) CF₃CHFCF₃ → CF₃CFCF₂ + HF, a four-center HF elimination pathway, and (2) CF₃CHFCF₃ → CF₃CHF + CF₃, a C−C bond fission pathway. The best estimate of the Δ<i>H</i>_r,298 for these processes are 34.8 and 92.3 kcal/mol using QCISD(T)/6-311G(d,p)//UMP2/6-31G(d) methods, respectively. The barrier for CF₃CHFCF₃ → CF₃CFCF₂ + HF was found to be 79.5 kcal/mol using the same methods. These results are discussed in light of past and current laboratory studies.