Reactivity of gas-phase anions with fully halogenated alkanes
作者:
RobertA. Morris,
A.A. Viggiano,
JohnF. Paulson,
期刊:
International Reviews in Physical Chemistry
(Taylor Available online 1996)
卷期:
Volume 15,
issue 1
页码: 183-204
ISSN:0144-235X
年代: 1996
DOI:10.1080/01442359609353180
出版商: Taylor & Francis Group
数据来源: Taylor
摘要:
Gas-phase reactivity of negative ions with fully halogenated alkanes is reviewed, restricted to rate constant measurements under thermal conditions. Reactivity generally increases upon substitution by heavier halogens. Perfluorocarbons (PFCs) are generally unreactive with negative ions, but the highly reactive O−anion reacts with the larger PFCs through multiple product channels. The trifluoromethyl halide series CF3X (X = Cl, Br, I) has been well-studied, and the reactions tend to be fast when nondissociative electron transfer to the halocarbon would be exothermic, regardless of the actual resulting product channels. For many of the reactions of CF3X and other perhaloalkanes, reactivity correlates with both the electron affinities and the electron attachment rates of the perhaloalkanes, though notable exceptions exist. This and other evidence suggests that many of the reactions are initiated by electron transfer to the halocarbon, which tends to explain why the reactivity of CF3X generally increases in the order Cl < Br < I for second-order reactions. The same reactivity trend in third-order association reactions is explained by the corresponding trends in CF3X dipole moment and polarizability. The results of several studies show that negative ion reactions are not a significant removal process for halocarbons in the atmosphere.
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