Ab initio study of naphthalene formation by addition of vinylacetylene to phenyl

Reaction pathways leading to the formation of naphthalene by the addition of vinylacetylene to phenyl were examined using density functional theory B3-LYP functionals with the standard triple-zeta basis set, 6-311G(d,p). The chemically activated reaction dynamics were examined employing time-dependent solution of master equations. The addition of phenyl to the triple bond of vinylacetylene was computed to be relatively slow, due to a substantial energy barrier of the intermediate rotation about the double bond. Addition of phenyl to die other end of a vinylacetylene molecule produced equally low rate constants. The most promising pathway appeared to be a two-step reaction sequence via the formation of phenyl-C4H3 molecules. The reaction rate evaluated for this pathway was very close to the value tested in prior flame simulations that demonstrated a dominant character of such a step for naphthalene fonnation. This indicates that the formation of naphthalene from phenyl and vinylacetylene may play a significant role in flame modeling of aromatic growth, and that the more favorable mechanism of the reaction may be a two-step sequence via the formation of a stable molecular intermediate rather than a "single" chemically activated path. The time-dependent solution of master equations revealed that at flame conditions typical of aromatic growth, the reaction system does not attain a steady state on a timescale of 1 ms. suggesting that dynamics of energy redistribution in such "elementary" reaction systems may need to be treated with inclusion of bimolecular reactions between energized adducts and gaseous partners.