Reaction of phenyl radicals with propyne.

The potential energy surface (PES) for the phenyl + propyne reaction, which might contribute to the growth of polycyclic aromatic hydrocarbons (PAHs) under a wide variety of reaction conditions, is described. The PES was characterized at the B3LYP-DFT/6-31G(d) and B3LYP-DFT/6-311+G(d,p) levels of theory. The energies of the entrance transition states, a direct hydrogen-transfer channel and two addition reactions leading to chemically activated C(9)H(9) intermediates, were also evaluated at the QCISD(T)/ 6-311G(d,p) and CCSD(T)/6-311G(d,p) levels of theory. An extensive set of unimolecular reactions was examined for these activated C(9)H(9)(dagger) intermediates, comprising 70 equilibrium structures and over 150 transition states, and product formation channels leading to substituted acetylenes and allenes such as PhCCH, PhCCCH(3), and PhCHCCH(2) were identified. The lowest energy pathway leads to indene, a prototype PAH molecule containing a five-membered ring. The title reaction thus is an example of possible direct formation of a PAH containing a five-membered ring, necessary to explain formation of nonplanar PAH structures, from an aromatic radical unit and an unsaturated hydrocarbon bearing an odd number of carbons. Extensive Supporting Information is available.