Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, P.O. Box 9513, NL 2300 RA Leiden, The Netherlands.
Phys Chem Chem Phys. 2018 Dec 5;20(47):29910-29917. doi: 10.1039/c8cp05830j.
A solid understanding of and a reliable model for the formation pathways of polycyclic aromatic (nitrogen containing) hydrocarbons (PA(N)Hs) is needed to account for their abundance in the interstellar medium and in Titan's atmosphere as well as to mitigate the emission of these carcinogens in our terrestrial environment. We have investigated the phenyl + acrylonitrile reaction mechanism between 600 and 1200 K in a hot microreactor. Radical intermediates (C9H8N˙), formed by addition, and closed-shell C9H7N products, formed by subsequent hydrogen elimination, are isomer-selectively identified using photoion mass-selected threshold photoelectron spectroscopy in conjunction with Franck-Condon simulations. Although quinoline is the most stable product, the calculated potential energy surface and a kinetic model confirm that the reaction is kinetically controlled and yields four open-chain isomers instead. The absence of quinoline is in stark contrast with the isoelectronic phenyl + vinylacetylene reaction that produces naphthalene. Ab initio calculations suggest that this change is brought about by the stability of the nitrile group, which inhibits ring formation. Therefore, it is unlikely that nitrile precursors form nitrogen-containing rings, which calls for alternative pathways by which nitrogen atoms can be incorporated in aromatic systems to explain their presence in the ISM and Titan's atmosphere.
需要深入了解并建立可靠的模型，以解释多环芳香（含氮）烃（PA（N）Hs）的形成途径，这不仅有助于解释它们在星际介质和土卫六大气中的丰富度，还有助于减轻这些致癌物质在我们地球环境中的排放。我们在热微反应器中研究了 600 到 1200 K 之间的苯基+丙烯腈反应机制。通过添加形成的自由基中间体（C9H8N˙），以及通过随后的氢消除形成的闭合壳层 C9H7N 产物，使用光离子质量选择的阈光电离光谱学结合 Franck-Condon 模拟，对其进行了异构体选择性识别。尽管喹啉是最稳定的产物，但计算出的势能面和动力学模型证实，该反应受动力学控制，生成四个开链异构体。这与生成萘的等电子苯基+乙烯基乙炔反应形成鲜明对比，因为后者不存在喹啉。从头算计算表明，这种变化是由于腈基的稳定性引起的，它抑制了环的形成。因此，氮原子不太可能通过腈前体形成含氮环，这就需要通过其他途径将氮原子纳入芳香体系，以解释它们在星际介质和土卫六大气中的存在。
