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

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 ( ) 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-1 H -indene ( p1 ) and 5-methyl-1 H -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. Flux contour map for the reactions of the p -tolyl radical with allene-d4 and methylacetylene-d4 at collision energies of around 48 kJ mol −1 .