Selected Ion Flow Tube Study of the Gas-Phase Reactions of CF+, CF2+, CF3+, and C2F4+ with C2H4<

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• 作者：Matthew J. Simpson ; Richard P. Tuckett
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：August 9, 2012
• 年：2012
• 卷：116
• 期：31
• 页码：8119-8129
• 全文大小：380K
• 年卷期：v.116,no.31(August 9, 2012)
• ISSN：1520-5215

文摘

We study how the degree of fluorine substitution for hydrogen atoms in ethene affects its reactivity in the gas phase. The reactions of a series of small fluorocarbon cations (CF⁺, CF₂⁺, CF₃⁺, and C₂F₄⁺) with ethene (C₂H₄), monofluoroethene (C₂H₃F), 1,1-difluoroethene (CH₂CF₂), and trifluoroethene (C₂HF₃) have been studied in a selected ion flow tube. Rate coefficients and product cations with their branching ratios were determined at 298 K. Because the recombination energy of CF₂⁺ exceeds the ionization energy of all four substituted ethenes, the reactions of this ion produce predominantly the products of nondissociative charge transfer. With their lower recombination energies, charge transfer in the reactions of CF⁺, CF₃⁺, and C₂F₄⁺ is always endothermic, so products can only be produced by reactions in which bonds form and break within a complex. The trends observed in the results of the reactions of CF⁺ and CF₃⁺ may partially be explained by the changing value of the dipole moment of the three fluoroethenes, where the cation preferentially attacks the more nucleophilic part of the molecule. Reactions of CF₃⁺ and C₂F₄⁺ are significantly slower than those of CF⁺ and CF₂⁺, with adducts being formed with the former cations. The reactions of C₂F₄⁺ with the four neutral titled molecules are complex, giving a range of products. All can be characterized by a common first step in the mechanism in which a four-carbon chain intermediate is formed. Thereafter, arrow-pushing mechanisms as used by organic chemists can explain a number of the different products. Using the stationary electron convention, an upper limit for 螖_fH掳₂₉₈(C₃F₂H₃⁺, with structure CF₂鈺怌H鈥擟H₂⁺) of 628 kJ mol^鈥? and a lower limit for 螖_fH掳₂₉₈(C₂F₂H⁺, with structure CF₂鈺怌H⁺) of 845 kJ mol^鈥? are determined.