title: First ring formation by radical addition of propargyl to but-1-ene-3-yne in combustion. Theoretical study of the C7H7 radical system.
abstract: Combustive formation of a first carbon ring is an important step in the growth of polycyclic aromatic hydrocarbons (PAHs) and soot platelets. Propargyl radical addition to but-1-ene-3-yne (vinylacetylene) can start this process, possibly forming 5-, 6-, and 7-membered rings. A variety of partially intertwined reaction pathways results from density functional theory (DFT), which indicates three C7H7 radicals, benzyl, tropyl, and vinylcyclopentadienyl, as particularly stable. DFT energetics forms a basis for a subsequent Rice-Ramsperger-Kassel-Marcus (RRKM) study at different combustion pressures and temperatures (P = 30-0.01 atm; T = 1200-2400 K). RRKM indicates open-chain structures and 5-rings as the most important products. Open-chain structures, whose main contributors are the initial adducts, are favored by lower T and higher P, while 5-rings are favored by higher T and lower P. The main feature is that the declining yield in open-chain structures with rising T almost mirrors, at all pressures, the growth with T exhibited by 5-rings (main contributor: fulvenallene). Thus, the two yield lines for open chains and 5-rings cross at some T, and their crossing moves toward lower T values as lower P values are considered. Because the T dependence of the yields (slope of the lines) is more pronounced in the T range close to the line crossing, it also becomes less pronounced at the lowest P values considered because the crossing region falls at very low T values. Another constant trait is that 6-rings (mainly benzyl radical) are the third contributor, though they are present at most with a modest maximum yield of 2.4-2.7% in a T range which moves toward lower T as P is reduced.
authors.affiliation: Dipartimento di Chimica, Università di Torino , Corso Massimo D'Azeglio 48, I-10125 Torino, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Trogolo
authors.forename: Andrea
authors.initials: A
authors.lastname: Maranzana
authors.forename: Giovanni
authors.initials: G
authors.lastname: Ghigo
authors.forename: Glauco
authors.initials: G
authors.lastname: Tonachini
mesh_terms: D000114:Acetylene / Q000031:analogs & derivatives / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D009019:Morphinans / Q000737:chemistry*; D011084:Polycyclic Aromatic Hydrocarbons / Q000138:chemical synthesis* / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D005609:Free Radicals; D009019:Morphinans; C440369:N-propargyl; D011084:Polycyclic Aromatic Hydrocarbons; D000114:Acetylene