Brown Timothy M, Nestler Matthew J, Rossabi Samuel M, Heard George L, Setser D W, Holmes Bert E
Department of Chemistry, University of North Carolina-Asheville , One University Heights, Asheville, North Carolina 28804-8511, United States and.
Kansas State University , Manhattan, Kansas 66506, United States.
J Phys Chem A. 2015 Sep 10;119(36):9441-51. doi: 10.1021/acs.jpca.5b06638. Epub 2015 Sep 1.
Vibrationally excited CD3CHFCl molecules with 96 kcal mol(-1) of energy were generated by the recombination of CD3 and CHFCl radicals in a room-temperature bath gas. The four competing unimolecular decomposition reactions, namely, 1,1-HCl and 1,2-DCl elimination and 1,1-HF and 1,2-DF elimination, were observed, and the individual rate constants were measured. The product branching fractions are 0.60, 0.27, 0.09, and 0.04 for 1,2-DCl, 1,1-HCl, 1,2-DF, and 1,1-HF elimination, respectively. Electronic structure calculations were used to define models of the four transition states. The statistical rate constants calculated from these models were compared to the experimental rate constants. The assigned threshold energies with ±2 kcal mol(-1) uncertainty are 60, 72, 65, and 74 kcal mol(-1) for the 1,2-DCl, 1,1-HCl, 1,2-DF, and 1,1-HF reactions, respectively. The loose structure of the 1,1-HX transition states, which is exemplified by the order of magnitude larger pre-exponential factor relative to the 1,2-HX elimination reactions, compensates for the high threshold energy; thus, the 1,1-HX elimination reaction rates can compete with the 1,2-HX elimination reactions for high levels of vibrational excitation in CD3CHFCl. The 1,1-HCl and 1,1-HF reactions are observed via the CD2═CDF and CD2═CDCl products formed from isomerization of the CD3CF and CD3CCl carbenes. These D-atom migration reactions are discussed, and the possibility of tunneling is evaluated. The transition states developed from the 1,1-HCl and 1,1-HF reactions of CD3CHFCl are compared to models for the HCl and HF elimination reactions of CHF2Cl, CHFCl2, and CH2FCl.
在室温浴气中，通过CD3和CHFCl自由基的重组生成了能量为96千卡/摩尔的振动激发态CD3CHFCl分子。观察到了四个相互竞争的单分子分解反应，即1,1-HCl和1,2-DCl消除反应以及1,1-HF和1,2-DF消除反应，并测量了各个反应的速率常数。对于1,2-DCl、1,1-HCl、1,2-DF和1,1-HF消除反应，产物分支比分别为0.60、0.27、0.09和0.04。利用电子结构计算确定了四个过渡态的模型。将从这些模型计算出的统计速率常数与实验速率常数进行了比较。对于1,2-DCl、1,1-HCl、1,2-DF和1,1-HF反应，指定的阈值能量（不确定度为±2千卡/摩尔）分别为60、72、65和74千卡/摩尔。1,1-HX过渡态的松散结构，相对于1,2-HX消除反应，其预指数因子大一个数量级，弥补了高阈值能量；因此，对于CD3CHFCl中高水平的振动激发，1,1-HX消除反应速率可以与1,2-HX消除反应竞争。通过CD3CF和CD3CCl卡宾异构化形成的CD2═CDF和CD2═CDCl产物观察到了1,1-HCl和1,1-HF反应。讨论了这些D原子迁移反应，并评估了隧穿的可能性。将CD3CHFCl的1,1-HCl和1,1-HF反应所形成的过渡态与CHF2Cl、CHFCl2和CH2FCl的HCl和HF消除反应模型进行了比较。
