Formation of 5- and 6-methyl-1H-indene (C10H10) via the reactions of the para-tolyl radical (C6H4CH3) with allene (H2CCCH2) and methylacetylene (HCCCH3) under single collision conditions

Physical Chemistry Chemical Physics Pub Date: 2015-03-03 DOI: 10.1039/C4CP04288C

Abstract

The reactions of the p-tolyl radical with allene-d4 and methylacetylene-d4 as well as of the p-tolyl-d7 radical with methylacetylene-d1 and methylacetylene-d3 were carried out under single collision conditions at collision energies of 44–48 kJ mol?1 and combined with electronic structure and statistical (RRKM) calculations. Our experimental results indicated that the reactions of p-tolyl with allene-d4 and methylacetylene-d4 proceeded via indirect reaction dynamics with laboratory angular distributions spanning about 20° in the scattering plane. As a result, the center-of-mass translational energy distribution determined a reaction exoergicity of 149 ± 28 kJ mol?1 and exhibited a pronounced maximum at around 20 to 30 kJ mol?1. In addition, the center-of-mass angular flux distribution T(θ) depicted a forward–backward symmetry and indicated geometric constraints upon the decomposing complex(es). Combining with calculations, these results propose that the bicyclic polycyclic aromatic hydrocarbons, 6-methyl-1H-indene (p1) and 5-methyl-1H-indene (p2), are formed under single collision conditions at fractions of at least 85% in both reaction systems. For the p-tolyl–methylacetylene system, experiments with partially deuterated reactants also reveal the formation of a third isomer p5 (1-methyl-4-(1-propynyl)benzene) at levels of 5–10%, highlighting the importance in conducting reactions with partially deuterated reactants to elucidate the underlying reaction pathways comprehensively.

Graphical abstract: Formation of 5- and 6-methyl-1H-indene (C10H10) via the reactions of the para-tolyl radical (C6H4CH3) with allene (H2CCCH2) and methylacetylene (HCCCH3) under single collision conditions
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