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• Products of the Reactions of o-Benzyne with Ethene, Propene, and Acetylene: Mass Spectrometric and Quantum Chemical Studies

G. Friedrichs, E. Goos, J. Gripp, H. Nicken, J.-B. Schönborn, H. Vogel, F. Temps
Z. Phys. Chem. 223 (2009) 387-407.

 

The primary products of bimolecular reactions of the aryne ortho-benzyne, o-C6H4 (1,2-dehydrobenzene), with the prototypic hydrocarbons ethene, propene, and acetylene have been detected by molecular beam mass spectrometry at a combustion relevant temperature of T = 1475 K. o-Benzyne was produced by flash pyrolysis of phthalic anhydride in absence and in presence of the respective reactant. Potential reaction pathways of the addition reactions were investigated by quantum chemical calculations. The reaction pathways with biradical intermediates were found to be energetically more favorable than alternative quasi-concerted [2+1] cycloaddition and concerted H-transfer pathways. Bicyclic benzocyclobutene and benzocyclobutadiene were identified as the main products of the reactions with C2H4 and C2H2, respectively. In case of propene, the presence of an allylic H atom initiates a favorable ene-type reaction sequence yielding the open-chain product allylbenzene. Overall, hydrocarbon reactivity was found to increase in the order C2H2, CH2H4 to C3H8. The range of the determined bimolecular rate constants is comparable to the rate constants of the corresponding phenyl radical reactions and hence point out a potentially important role of o-C6H4 reactions in flame and soot formation chemistry.

 

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