HACA's Heritage: A Free‐Radical Pathway to Phenanthrene in Circumstellar Envelopes of Asymptotic Giant Branch Stars

• DOI: 10.1002/anie.201701259
• Publication Date: 2017-03-23T10:39:30Z
• Authors: Tao Yang; Ralf I. Kaiser; Tyler P. Troy; Bo Xu; Oleg Kostko; Musahid Ahmed; Alexander M. Mebel; Marsel V. Zagidullin; Valeriy N. Azyazov
• Keywords: Murchison meteorite; Acetylene

The hydrogen-abstraction/acetylene-addition (HACA) mechanism has been central for the last decades in attempting to rationalize formation of polycyclic aromatic hydrocarbons (PAHs) as detected carbonaceous meteorites such Murchison. Nevertheless, basic reaction mechanisms leading even simplest tricyclic PAHs like anthracene and phenanthrene are still elusive. Here, by exploring previously unknown chemistry ortho-biphenylyl radical with acetylene, we deliver compelling evidence on efficient synthesis carbon-rich circumstellar environments. However, lack isomer implies that HACA alone cannot be responsible extreme Considering overall picture, alternative pathways vinylacetylene-mediated reactions required play a crucial role complex envelopes dying stars.