Unimolecular Isomerization of CH2FCD2Cl via the Interchange of Cl and F Atoms: Assignment of the Threshold Energy to the 1,2-Dyotropic Rearrangement

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• 作者：Mary K. Tucker ; Samuel M. Rossabi ; Corey E. McClintock ; George L. Heard ; D. W. Setser ; Bert E. Holmes
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：August 8, 2013
• 年：2013
• 卷：117
• 期：31
• 页码：6717-6723
• 全文大小：273K
• 年卷期：v.117,no.31(August 8, 2013)
• ISSN：1520-5215

文摘

The room-temperature gas-phase recombination of CH₂F and CD₂Cl radicals was used to prepare CH₂FCD₂Cl molecules with 91 kcal mol^鈥? of vibrational energy. Three unimolecular processes are in competition with collisional deactivation of CH₂FCD₂Cl; HCl and DF elimination to give CHF鈺怌D₂ and CH₂鈺怌DCl plus isomerization to give CH₂ClCD₂F by the interchange of F and Cl atoms. The Cl/F interchange reaction was observed, and the rate constant was assigned from measurement of CHCl鈺怌D₂ as a product, which is formed by HF elimination from CH₂ClCD₂F. These experiments plus previously published results from chemically activated CH₂ClCH₂F and electronic structure and RRKM calculations for the kinetic-isotope effects permit assignment of the three rate constants for CH₂FCD₂Cl (and for CH₂ClCD₂F). The product branching ratio for the interchange reaction versus elimination is 0.24 卤 0.04. Comparison of the experimental rate constant with the RRKM calculated rate constant permitted the assignment of a threshold energy of 62 卤 3 kcal mol^鈥? for this type-1 dyotropic rearrangement. On the basis of electronic structure calculations, the nature of the transition state for the rearrangement reaction is discussed. The radical recombination reactions in the chemical system also generate vibrationally excited CD₂ClCD₂Cl and CH₂FCH₂F molecules, and the rate constants for DCl and HF elimination were measured in order to confirm that the photolysis of CD₂ClI and (CH₂F)₂CO mixtures was giving reliable data for CH₂FCD₂Cl.