Yang Zhenghai, Galimova Galiya R, He Chao, Goettl Shane J, Paul Dababrata, Lu Wenchao, Ahmed Musahid, Mebel Alexander M, Li Xiaohu, Kaiser Ralf I
Department of Chemistry, University of Hawaii at Manoa, 2545 McCarthy Mall, Honolulu, HI 96822, USA.
Department of Chemistry and Biochemistry, Florida International University, Miami, FL 33199, USA.
Sci Adv. 2023 Sep 8;9(36):eadi5060. doi: 10.1126/sciadv.adi5060.
The 1-indenyl (CH) radical, a prototype aromatic and resonantly stabilized free radical carrying a six- and a five-membered ring, has emerged as a fundamental molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures in deep space and combustion systems. However, the underlying formation mechanisms have remained elusive. Here, we reveal an unconventional low-temperature gas-phase formation of 1-indenyl via barrierless ring annulation involving reactions of atomic carbon [C(P)] with styrene (CHCH) and propargyl (CH) with phenyl (CH). Macroscopic environments like molecular clouds act as natural low-temperature laboratories, where rapid molecular mass growth to 1-indenyl and subsequently complex PAHs involving vinyl side-chained aromatics and aryl radicals can occur. These reactions may account for the formation of PAHs and their derivatives in the interstellar medium and carbonaceous chondrites and could close the gap of timescales of their production and destruction in our carbonaceous universe.
1-茚基（CH）自由基是一种典型的芳香族且具有共振稳定作用的自由基，带有一个六元环和一个五元环，已成为深空中非平面多环芳烃（PAHs）和碳质纳米结构以及燃烧系统的基本分子构建单元。然而，其潜在的形成机制仍然难以捉摸。在此，我们揭示了一种非常规的低温气相1-茚基形成过程，该过程通过无势垒的环化反应实现，涉及原子碳[C(P)]与苯乙烯（CHCH）以及炔丙基（CH）与苯基（CH）的反应。诸如分子云之类的宏观环境充当天然的低温实验室，在其中可以快速实现分子质量增长至1-茚基，随后形成涉及乙烯基侧链芳烃和芳基自由基的复杂多环芳烃。这些反应可能解释了星际介质和碳质球粒陨石中多环芳烃及其衍生物的形成，并可能弥合我们碳质宇宙中它们产生和破坏的时间尺度差距。
