Reactions of o-benzyne with propargyl and benzyl radicals: potential sources of polycyclic aromatic hydrocarbons in combustion

Abstract

The kinetics and mechanisms of the reactions of o-benzyne with propargyl and benzyl radicals have been investigated computationally. The possible reaction pathways have been explored by quantum chemical calculations at the M06-2X/6-311+G(3df,2p)//B3LYP/6-311G(d,p) level and the mechanisms have been investigated by the Rice-Ramsperger-Kassel-Marcus theory/master-equation calculations. It was found that the o-benzyne associates with the propargyl and benzyl radicals without pronounced barriers and the activated adducts easily isomerize to five-membered ring species. Indenyl radical and fluorene + H were predicted to be dominantly produced by the reactions of o-benzyne with propargyl and benzyl radicals, respectively, with the rate constants close to the high-pressure limits at temperatures below 2000 K. The related reactions on the two potential energy surfaces, namely, the reaction between fulvenallenyl radical and acetylene and the decomposition reactions of indenyl and α-phenylbenzyl radicals were also investigated. The high reactivity of o-benzyne toward the resonance stabilized radicals suggested a potential role of o-benzyne as a precursor of polycyclic aromatic hydrocarbons in combustion.

Rationalization of photo-detachment spectra of the indenyl anion (C9H7−) from the perspective of vibronic coupling theory

“…42,43 The formation of closed-shell indene (C 9 H 8 ) and its dehydrogenated radical [indenyl (C 9 H 7 )] species has been predicted from the addition of acetylene to fulvenallene, 44 cyclopentadienyl radical, 45 and benzyl radical. 46 Along with these, the addition of propargyl to benzyne 47 and the oxidation of the naphthyl radical followed by decomposition [48][49][50] also suggest the possible mechanism of formation of indenyl. Indenyl is also found as a product during the flow of acetylene over nano-sized silicate particles.…”

Slow photoelectron velocity-map imaging spectroscopy of the C9H7 (indenyl) and C13H9 (fluorenyl) anions

“…Various thermochemical and kinetic calculations have predicted the formation of indene or indenyl by acetylene addition to fulvenallene, 19 cyclopentadienyl radical, 20 and benzyl radical. 21,22 Other proposed mechanisms include the addition of propargyl to benzyne, 23 as well as the oxidation of naphthyl radical followed by decomposition to indenyl. 24,25 Indenyl has also been identified as a product when acetylene is passed over nano-sized silicate particles.…”

Multiphoton dissociation dynamics of the indenyl radical at 248 nm and 193 nm

“…20 da Silva et al 21 examined the reaction of fulvenallene (C7H 6 ) and C 2 H 2 leading to the formation of C 9 H 8 , which can lose a hydrogen atom to produce C 9 H7. An extensive theoretical study examining the C 9 H7 potential energy surface was undertaken by Matsugi and Miyoshi, 22 who determined the kinetics and mechanism of the benzyne (C 6 H 4 ) + propargyl (C 3 H 3 ) reaction. C 9 H7 participates as an intermediate species that can isomerize and then dissociate into acetylene and fulvenallenyl (C 2 H 2 + C7H5).…”

“…In this work, C 9 H7 photodissociation was investigated using fast beam photofragment translational spectroscopy at 248 nm and 193 nm. Equations (1)- (6) show the observable product channels at 193 nm (6.42 eV), not all of which are accessible at 248 nm (5.0 eV), [21][22][23][24][25][26]…”

“…Additionally, there are multiple two-and three-body product channels [Eqs. (7)- (13)] that are energetically inaccessible for one photon absorption at 248 nm or 193 nm, 5,6,21,22,[26][27][28][29][30]…”