The Unimolecular Reactions of CF3CHF2 Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules,The Journal of Physical Chemistry A

当前位置： X-MOL 学术 › J. Phys. Chem. A › 论文详情

Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)

The Unimolecular Reactions of CF3CHF2 Studied by Chemical Activation: Assignment of Rate Constants and Threshold Energies to the 1,2-H Atom Transfer, 1,1-HF and 1,2-HF Elimination Reactions, and the Dependence of Threshold Energies on the Number of F-Atom Substituents in the Fluoroethane Molecules
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2017-11-09 00:00:00 , DOI: 10.1021/acs.jpca.7b06769
Caleb A. Smith , Blanton R. Gillespie , George L. Heard , D. W. Setser ₁ , Bert E. Holmes

Affiliation

The recombination of CF₃ and CHF₂ radicals in a room-temperature bath gas was used to prepare vibrationally excited CF₃CHF₂* molecules with 101 kcal mol^–1 of vibrational energy. The subsequent 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions were observed as a function of bath gas pressure by following the CHF₃, CF₃(F)C: and C₂F₄ product concentrations by gas chromatography using a mass spectrometer as the detector. The singlet CF₃(F)C: concentration was measured by trapping the carbene with trans-2-butene. The experimental rate constants are 3.6 × 10⁴, 4.7 × 10⁴, and 1.1 × 10⁴ s^–1 for the 1,2-H atom transfer and 1,1-HF and 1,2-HF elimination reactions, respectively. These experimental rate constants were matched to statistical RRKM calculated rate constants to assign threshold energies (E₀) of 88 ± 2, 88 ± 2, and 87 ± 2 kcal mol^–1 to the three reactions. Pentafluoroethane is the only fluoroethane that has a competitive H atom transfer decomposition reaction, and it is the only example with 1,1-HF elimination being more important than 1,2-HF elimination. The trend of increasing threshold energies for both 1,1-HF and 1,2-HF processes with the number of F atoms in the fluoroethane molecule is summarized and investigated with electronic-structure calculations. Examination of the intrinsic reaction coordinate associated with the 1,1-HF elimination reaction found an adduct between CF₃(F)C: and HF in the exit channel with a dissociation energy of ∼5 kcal mol^–1. Hydrogen-bonded complexes between HF and the H atom migration transition state of CH₃(F)C: and the F atom migration transition state of CF₃(F)C: also were found by the calculations. The role that these carbene–HF complexes could play in 1,1-HF elimination reactions is discussed.

中文翻译：

通过化学活化研究CF ₃ CHF ₂的单分子反应：将速率常数和阈值能量分配给1,2-H原子转移，1,1-HF和1,2-HF消除反应以及阈值能量的依赖性氟乙烷分子中F-原子取代基的数量

CF ₃和CHF ₂自由基在室温浴气体中的重组用于制备振动能为101 kcal mol ^–1的振动激发CF ₃ CHF ₂ *分子。通过遵循CHF ₃，CF ₃（F）C：和C ₂ F ₄，观察到随后的1,2-H原子转移以及1,1-HF和1,2-HF消除反应与浴气压的关系。使用质谱仪作为检测器，通过气相色谱法测定产物浓度。单线态CF ₃（F）C：通过反式捕获卡宾来测量浓度-2-丁烯。实验速率常数是3.6×10 ⁴，4.7×10 ⁴和1.1×10 ⁴小号^-1分别为1,2-H原子转移和1,1- HF和1,2- HF消除反应，。将这些实验速率常数与RRKM计算的速率常数进行统计，以指定阈值能量（E ₀）为88±2、88±2和87±2 kcal mol ^–1对这三个反应。五氟乙烷是唯一具有竞争性H原子转移分解反应的氟乙烷，并且它是唯一一个1,1,2-HF消除比1,2-HF消除更重要的例子。总结并研究了随着氟乙烷分子中F原子数目的增加，随着1,1-HF和1,2-HF过程阈值能量的增加趋势，并通过电子结构计算进行了研究。检查与1,1-HF消除反应相关的本征反应坐标，发现CF ₃（F）C：与HF在出口通道中的加合物具有约5 kcal mol ^–1的离解能。HF与CH ₃的H原子迁移过渡态之间的氢键配合物通过计算还发现了（F）C：和CF ₃（F）C：的F原子迁移过渡态。讨论了这些卡宾-HF络合物在1,1-HF消除反应中的作用。

更新日期：2017-11-09

点击分享查看原文

点击收藏

阅读更多本刊最新论文