Kinetics of CN reactions with allene, butadiene, propylene and acrylonitrile

The two-laser pump-probe technique has been used to study the kinetics of the reaction of CN radicals with C₃H₆, CD₃C₂H₃, C₃D₆, C₂H₃CN, C₃H₄ and C₄H₆ at temperatures between 297 and 740 K. CN was generaged by 248-nm photolysis of ICN. Laser-induced fluorescence of the CN radical has been used for its detection by CN (B←X) excitation. The values for the rate constants, given in units of cm³/s, are reported as: k(C₃H₆)=10^-9.88±0.10exp(+244 ±96.3/T), k(C₃H₃D₃) = 10^{-9.76±0.04 exp (+143.4±35.1/T), k(C₃D₆)=10-9.87±0.05exp(+231. 4±47.01/T, k(C₂H₃CN)=10-10.52±0.02exp(+103. 6±20.3/T), k(C₃H₄)=10-9.58±0.08} ×exp(+167.4±73.7/T), k(C₄H₆)=10^-9.59±0.04exp(+169. 2±33.1/T). The absolute rates of CN reactions with CH₃CHCH₂, CD₃CHCH₂ and CD₃CDCD₂ are essentially the same and are somewhat faster than that of the CN+C₂H₄ reaction. This suggests that the CN+C₃H₆ reaction occurs primarily by addition to the unsaturated bond and the CH₃ group enhances the addition process slightly. The rate of the CN+CH₂CHCN reaction, however, was found to be a factor of six slower than that of CN+C₂H₄, indicating a substantial electron withdrawing effect of the CN group in vinyl cyanide which results in the reduction in the addition rate. The rates for CN reaction with CH₂CCH₂ and CH₂CHCHCH₂ are approximately the same and are twice that of CN+C₂H₄.