Theoretical study on the HACA chemistry of naphthalenyl radicals and acetylene: The formation of C12H8, C14H8, and C14H10 species. Issue 11 (6th July 2020) - Chu, Te‐Chun
Abstract: The hydrogen‐abstraction‐C2 H2 ‐addition (HACA) chemistry of naphthalenyl radicals has been studied extensively, but there is a significant discrepancy in product distributions reported or predicted in literature regarding appearance of C14 H8 and C14 H10 species. Starting from ab initio calculations, a comprehensive theoretical model describing the HACA chemistry of both 1‐ and 2‐naphthalenyl radicals is generated. Pressure‐dependent kinetics are considered in the C12 H9, C14 H9, and C14 H11 potential energy surfaces including formally direct well‐skipping pathways. On the C12 H9 PES, reaction pathways were found connecting two entry points: 1‐naphthalenyl (1‐C10 H7 ) + acetylene (C2 H2 ) and 2‐C10 H7 + C2 H2 . A significant amount of acenaphthylene is predicted to be formed from 2‐C10 H7 + C2 H2, and the appearance of C14 H8 isomers is predicted in the model simulation, consistent with high‐temperature experimental results from Parker et al. At 1500 K, 1‐C10 H7 + C2 H2 mostly generates acenaphthylene through a formally direct pathway, which predicted selectivity of 66% at 30 Torr and 56% at 300 Torr. The reaction of 2‐C10 H7 with C2 H2 at 1500 K yields 2‐ethynylnaphthalene as the most dominant product, followed by acenaphthylene mainly generated via isomerization of 2‐C10 H7 to 1‐C10 H7 . Both the 1‐C10 H7 and 2‐C10 H7 reactions with C2 H2 form some C14 H8 products, but negligible phenanthrene and anthracene formation is predicted at 1500 K. A rate‐of‐production analysis reveals that C14 H8 formation is strongly affected by the rates of H‐abstraction from acenaphthylene, 1‐ethynylnaphthalene, and 2‐ethynylnaphthalene, so the kinetics of these reactions are accurately calculated at the high level G3(MP2, CC)//B3LYP/6‐311G ** level of theory. At intermediate temperatures like 800 K, acenaphthylene + H are the leading bimolecular products of 1‐C10 H7 + C2 H2, and 1‐acenaphthenyl radical is the most abundant C12 H9 isomer due to its stability. The predicted product distribution of 2‐C10 H7 + C2 H2 at 800 K, in contrast to the results of Parker et al is predicted to consist primarily of species containing three fused benzene rings—for example, phenanthrene and anthracene—as the leading products, indicating HACA chemistry is valid from two to three ring polycyclic aromatic hydrocarbons under some conditions. Further experiments are needed for validation.