Formation of five-membered ring structures via reactions of o-benzyne

• Published in: Proceedings of the Combustion Institute 2024, Vol.40 (1-4), p.105623, Article 105623
• Main Authors: Hansen, Nils, Bierkandt, Thomas, Gaiser, Nina, Oßwald, Patrick, Köhler, Markus, Hemberger, Patrick
• Format: Article
• Language: English
• Subjects: Molecular-weight growth; o-Benyzne; Polycyclic aromatic hydrocarbons (PAHs); Propargyl; Threshold photoelectron spectroscopy (TPES)
• ISSN: 1540-7489; 1873-2704
• DOI: 10.1016/j.proci.2024.105623

The formation of five-membered ring structures is important for the generation of curved and bowl-shaped polycyclic aromatic hydrocarbons (PAHs) under combustion conditions. Here, we report the identification of the indenyl (C9H7) radical – the simplest aromatic hydrocarbon radical carrying an adjacent five- and six-membered ring, as the major product of the o-benzyne (o-C6H4) reaction with propargyl (C3H3). Because real flames exhibit a complex chemistry, elucidation of a specific reaction is very challenging. Instead, we studied the o-C6H4 + C3H3 reaction in a resistively heated microtubular SiC reactor at controlled conditions of 1150 K and a pressure near 10–20 Torr. To this end, the reactants o-benzyne and propargyl were pyrolytically generated from benzoyl chloride and propargyl bromide. We identified the reactants and the indenyl radical isomer-selectively utilizing photoion mass-selected threshold photoelectron spectroscopy (ms-TPES). The experimentally observed predominant formation of indenyl radicals finally confirms the theoretical predictions of Matsugi and Miyoshi [Phys. Chem. Chem. Phys. 14 (2012), 9722–9728] and highlights a versatile route for the formation of five-membered rings and curved PAHs via reactions of o-benzyne that favor the formation of multiring species over aliphatically substituted aromatic species.