Reactions of CN and C2H Radicals

FIGURE 11.10 Products formed in the reactions of ethynyl and cyano radicals with unsaturated hydrocarbon molecules under single collision conditions. The reaction of ethynyl radicals with benzene is currently being studied in our laboratory. 

It should be stressed that in case of the ethynyl-acetylene reaction, a molecular hydrogen loss channel synthesizing the 1,3-butadienyl radical is open as well. Since the reactions of cyano and ethynyl radicals have no entrance barrier, are exoergic, and aU transition states involved are lower than the energy of the separated reactants, these reaction classes are extremely important to form nitriles and complex unsaturated hydrocarbons in low-temperature environments. On the other hand, the corresponding phenyl radical reactions are—due to the presence of an entrance barrier—closed in those environments. However, the elevated temperature in combustion systems helps to overcome these barriers, thus making phenyl radical reactions important pathways to form aromatic molecules in combustion flames. 

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Carty D, Le Page V, Sims IR, Smith IWM. (2001) Low temperature rate coefficients for the reactions of CN and C2H radicals with aUene (CH2=C=CH2) and methyl acetylene (CH3C = CH). Chem. Phys. Lett. 344 310-316. 

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