First aromatic ring formation by the radical-chain reaction of vinylacetylene and propargyl

Recent investigations illustrated that clustering of hydrocarbons by radical-chain reaction (CHRCR) mechanism provides key mechanistic steps for the rapid synthesis of polycyclic aromatic hydrocarbons (PAHs) and soot. Resonance-stabilized radicals (RSRs) play critical roles in this mechanism, and non-benzene first-ring species have attracted considerable attention as precursors of larger aromatic hydrocarbons. C7H7 RSRs, such as benzyl, tropyl, vinyl-cyclopentadienyl, are particularly stable and are thus quite important in the growth of PAHs. The addition of vinylacetylene to propargyl radical, a prototypical CHRCR reaction, provides a facile route to C7H7 RSRs. We have directly investigated the reaction of propargyl and vinylacetylene in isomer-resolved elementary experiments by synchrotron vacuum ultra-violet photoionization molecular beam mass spectrometry (SVUV-PI-MBMS). In good agreement with theoretical predictions, vinyl-cyclopentadienyl is found to be the major product of vinylacetylene and propargyl reaction while benzyl is minor. This work demonstrates a feasible CHRCR pathway, not proceeding through benzene, for PAH formation. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

Recent investigations have shown that the clustering of hydrocarbons by radical-chain reaction (CHRCR) mechanism is crucial for the rapid synthesis of polycyclic aromatic hydrocarbons (PAHs) and soot. Resonance-stabilized radicals (RSRs) are essential in this mechanism, with non-benzene first-ring species being significant as precursors of larger aromatic hydrocarbons. Stable C7H7 RSRs, such as benzyl, tropyl, and vinyl-cyclopentadienyl, are key in the growth of PAHs.