Velocity Map Imaging Study of Ion–Radical Chemistry: Charge Transfer and Carbon–Carbon Bond Formation in the Reactions of Allyl Radicals with C+

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• 作者：Linsen Pei ; James M. Farrar
• 刊名：Journal of Physical Chemistry A
• 出版年：2016
• 出版时间：August 11, 2016
• 年：2016
• 卷：120
• 期：31
• 页码：6122-6128
• 全文大小：381K
• 年卷期：0
• ISSN：1520-5215

文摘

We present an experimental and computational study of the dynamics of collisions of ground state carbon cations with allyl radicals, C₃H₅, at a collision energy of 2.2 eV. Charge transfer to produce the allyl cation, C₃H₅⁺, is exoergic by 3.08 eV and proceeds via energy resonance such that the electron transfer occurs without a significant change in nuclear velocities. The products have sufficient energy to undergo the dissociation process C₃H₅⁺ → C₃H₄⁺ + H. Approximately 80% of the reaction products are ascribed to charge transfer, with ∼40% of those products decaying via loss of a hydrogen atom. We also observe products arising from the formation of new carbon–carbon bonds. The experimental velocity space flux distributions for the four-carbon products are symmetric about the centroid of the reactants, providing direct evidence that the products are mediated by formation of a C₄H₅⁺ complex living at least a few rotational periods. The primary four-carbon reaction products are formed by elimination of molecular hydrogen from the C₄H₅⁺ complex. More than 75% of the nascent C₄H₃⁺ products decay by C–H bond cleavage to yield a C₄H₂⁺ species. Quantum chemical calculations at the MP2/6-311+g(d,p) level of theory support the formation of a nonplanar cyclic C₄H₅⁺ adduct that is produced when the p-orbital containing the unpaired electron on C⁺ overlaps with the unpaired spin density on the terminal carbon atoms in allyl. Product formation then occurs by 1,2-elimination of molecular hydrogen from the cyclic intermediate to form a planar cyclic C₄H₃⁺ product. The large rearrangement in geometry as the C₄H₃⁺ products are formed is consistent with high vibrational excitation in that product and supports the observation that the majority of those products decay to form the C₄H₂⁺ species.