Rate constants for the reactions of CN with C6–C8 unsaturated hydrocarbons: the relations between the reaction rates and the molecular lengths

Rates of CN reactions with 1,3,5-hexatriene and three octadiynes have been measured at various sample pressures using laser-induced fluorescence of the CN radical. The rate constants are, in units of cm3 molecule−1 s−1, k1,3,5-hexatriene=(6.7±0.2)×10−10, k1,7-octadiyne=(3.5±0.3)×10−10, k2,6-octadiyne=(2.4±0.3)×10−10 and k3,5-octadiyne=(2.5±0.3)×10−10, respectively. It shows clearly that two factors which influence the reaction rates of CN with unsaturated hydrocarbons are important. One is the length of π-conjugated system, the other is the difference between elimination processes after CN insertion.