Co-pyrolysis of 1-naphthylmethyl radical with allene and propyne: Radical-molecule (C3H4) vs. radical-radical (C3H3) reaction pathways

In this work, we conducted a combined experimental and theoretical investigation into the reactivity of naphthylmethyl radical (1-A2CH 2 , C 11 H 9 ) with allene (aC 3 H 4 ) and propyne (pC 3 H 4 ). Co-pyrolysis experiments of 1-(chloromethyl)naphthalene (1-A2CH 2 Cl) with aC 3 H 4 or pC 3 H 4 were studied using a flash pyrolysis microreactor coupled with synchrotron vacuum ultraviolet photoionization mass spectrometry. Significant signals at m/z = 39 (C 3 H 3 ), attributed to the rapid H-abstraction and/or pyrolysis of C 3 H 4 molecules, were detected in both experiments, indicating concurrent radical-radical (1-A2CH 2 + C 3 H 3 ) and radical-molecule (1-A2CH 2 + aC 3 H 4 /pC 3 H 4 ) reactions. Theoretical calculations reveal that the radical-radical reaction is kinetically favored under experimental conditions compared to the radical-molecule reaction, dominantly forming two C 14 H 12 adducts, 1-(1,2-butadiene-4-yl)naphthalene (1-W1) and 1-(but‑yn-3-yl)naphthalene (1-W2), along with minor amounts of other C 14 H 12 isomers and C 14 H 11 + H products. The computed rate coefficients and branching ratios of various reaction channels expand the analysis to broader temperature and pressure ranges. The radical-radical products (1-W1 and 1-W2) dominate at atmospheric-to-high pressures (>1 atm) or relatively lower temperatures (<1500 K). At higher temperatures and low pressures, competition arises between radical-radical and radical-molecule pathways. Furthermore, the structures of bimolecular products differ significantly between the 1-A2CH 2 + aC 3 H 4 and 1-A2CH 2 + pC 3 H 4 reaction systems, with implications for the formation of larger polycyclic aromatic hydrocarbons.