Department of Chemistry, University of Hawai'i at Manoa, Honolulu, HI, 96822, USA.
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
Angew Chem Int Ed Engl. 2017 Apr 10;56(16):4515-4519. doi: 10.1002/anie.201701259. Epub 2017 Mar 22.
The hydrogen-abstraction/acetylene-addition (HACA) mechanism has been central for the last decades in attempting to rationalize the formation of polycyclic aromatic hydrocarbons (PAHs) as detected in carbonaceous meteorites such as in Murchison. Nevertheless, the basic reaction mechanisms leading to the formation of even the simplest tricyclic PAHs like anthracene and phenanthrene are still elusive. Here, by exploring the previously unknown chemistry of the ortho-biphenylyl radical with acetylene, we deliver compelling evidence on the efficient synthesis of phenanthrene in carbon-rich circumstellar environments. However, the lack of formation of the anthracene isomer implies that HACA alone cannot be responsible for the formation of PAHs in extreme environments. Considering the overall picture, alternative pathways such as vinylacetylene-mediated reactions are required to play a crucial role in the synthesis of complex PAHs in circumstellar envelopes of dying carbon-rich stars.
氢提取/乙炔加成（HACA）机制在过去几十年中一直是尝试合理化多环芳烃（PAHs）形成的核心，这些 PAHs 如在默奇森陨石中检测到的那样。然而，导致甚至最简单的三环 PAHs 如蒽和菲形成的基本反应机制仍然难以捉摸。在这里，通过探索以前未知的邻联苯自由基与乙炔的化学性质，我们提供了令人信服的证据，证明在富碳的星际环境中有效地合成了菲。然而，蒽异构体的缺乏形成意味着 HACA 本身不能为极端环境中 PAHs 的形成负责。考虑到整体情况，需要乙烯基乙炔介导的反应等替代途径在富碳恒星垂死的星际包层中复杂 PAHs 的合成中发挥关键作用。
