A theoretical analysis of the reaction between propargyl and molecular oxygen

The temperature- and pressure-dependent kinetics of the reaction between pr opargyl and molecular oxygen have been studied with a combination of electr onic structure theory, transition state theory, and the time-dependent mast er equation. The stationary points on the potential energy surface were loc ated with B3LYP density functional theory. Approximate QCISD(T,Full)/6-311+G(3df,2pd) energies were obtained at these stationary points. At low tempe ratures the reaction is dominated by addition to the CH2 side of the propar gyl radical followed by stabilization. However, addition to the CH side, wh ich is followed by one of various possible internal rearrangements, becomes the dominant process at higher temperatures. These internal rearrangements involve a splitting of the O-2 bond via the formation of 3-, 4- or 5-membe red rings, with the apparent products being CH2CO + HCO. Rearrangement via the 3-membered ring is found to dominate the kinetics. Rearrangement from t he CH2 addition product, via a 4-membered ring, would yield H2CO + HCCO, bu t the barrier to this rearrangement is too high to be kinetically significa nt. Other possible products require H transfers and, as a result, appear to be kinetically irrelevant. Modest variations in the energetics of a few ke y stationary points (most notably the entrance barrier heights) yield kinet ic results that are in good agreement with the experimental results of Slag le and Gutman (I. R. Slagle and D. Gutman, Proc. Combust. Inst., 1986, 21, 875) and of Atkinson and Hudgens (D. B. Atkinson and J. W. Hudgens, J. Phys . Chem. A, 1999, 103, 4242).