Department of Chemistry, University of North Carolina-Asheville, Asheville, North Carolina 28804-8511, USA.
J Phys Chem A. 2011 Feb 17;115(6):1054-62. doi: 10.1021/jp108955m. Epub 2011 Jan 18.
The recombination of CF(2)Cl and CH(2)F radicals was used to prepare CF(2)ClCH(2)F* molecules with 93 ± 2 kcal mol(-1) of vibrational energy in a room temperature bath gas. The observed unimolecular reactions in order of relative importance were: (1) 1,2-ClH elimination to give CF(2)═CHF, (2) isomerization to CF(3)CH(2)Cl by the interchange of F and Cl atoms and (3) 1,2-FH elimination to give E- and Z-CFCl═CHF. Since the isomerization reaction is 12 kcal mol(-1) exothermic, the CF(3)CH(2)Cl* molecules have 105 kcal mol(-1) of internal energy and they can eliminate HF to give CF(2)═CHCl, decompose by rupture of the C-Cl bond, or isomerize back to CF(2)ClCH(2)F. These data, which provide experimental rate constants, are combined with previously published results for chemically activated CF(3)CH(2)Cl* formed by the recombination of CF(3) and CH(2)Cl radicals to provide a comprehensive view of the CF(3)CH(2)Cl* ↔ CF(2)ClCH(2)F* unimolecular reaction system. The experimental rate constants are matched to calculated statistical rate constants to assign threshold energies for the observed reactions. The models for the molecules and transition states needed for the rate constant calculations were obtained from electronic structures calculated from density functional theory. The previously proposed explanation for the formation of CF(2)═CHF in thermal and infrared multiphoton excitation studies of CF(3)CH(2)Cl, which was 2,2-HCl elimination from CF(3)CH(2)Cl followed by migration of the F atom in CF(3)CH, should be replaced by the Cl/F interchange reaction followed by a conventional 1,2-ClH elimination from CF(2)ClCH(2)F. The unimolecular reactions are augmented by free-radical chemistry initiated by reactions of Cl and F atoms in the thermal decomposition of CF(3)CH(2)Cl and CF(2)ClCH(2)F.
CF(2)Cl 和 CH(2)F 自由基的复合用于在室温浴气中制备具有 93 ± 2 kcal mol(-1)振动能的 CF(2)ClCH(2)F分子。按照相对重要性的顺序观察到的单一分子反应为：(1)1,2-ClH 消除生成 CF(2)═CHF，(2)通过 F 和 Cl 原子的交换异构化为 CF(3)CH(2)Cl，以及(3)1,2-FH 消除生成 E-和 Z-CFCl═CHF。由于异构化反应放热 12 kcal mol(-1)，因此 CF(3)CH(2)Cl分子具有 105 kcal mol(-1)的内部能量，它们可以消除 HF 生成 CF(2)═CHCl，通过 C-Cl 键断裂分解，或者异构化为 CF(2)ClCH(2)F。这些数据提供了实验速率常数，与以前发表的关于由 CF(3)和 CH(2)Cl 自由基复合形成的化学活化 CF(3)CH(2)Cl的结果相结合，提供了 CF(3)CH(2)Cl↔CF(2)ClCH(2)F*单一分子反应系统的全面视图。实验速率常数与计算统计速率常数相匹配，为观察到的反应分配阈值能量。用于速率常数计算的分子和过渡态模型是从密度泛函理论计算的电子结构中获得的。对于在 CF(3)CH(2)Cl 的热和红外多光子激发研究中形成 CF(2)═CHF 的先前提出的解释，即 CF(3)CH(2)Cl 中 2,2-HCl 的消除，随后是 F 原子在 CF(3)CH 中的迁移，应该被 CF(2)ClCH(2)F 中 Cl/F 交换反应随后是常规的 1,2-ClH 消除所取代。自由基化学通过 CF(3)CH(2)Cl 和 CF(2)ClCH(2)F 热分解中 Cl 和 F 原子的反应引发单一分子反应。
