Effect of Structure on the Rate Constants for Reaction of NO3Radicals with a Series of Linear and Branched C5−C71-Alkenes at 296 ± 2 K

Abstract

Rate constants for the gas-phase reactions of NO3 radicals with 13 linear and branched C5-C7 1-alkenes, CH2═CHR, where R = alkyl, have been measured at 296 ± 2 K and atmospheric pressure of air by a relative rate method. 1-Butene was used as the reference compound, and the rate constants obtained (in units of 10(-14) cm(3) molecule(-1) s(-1)) were as follows: 1-pentene, 1.50 ± 0.07; 1-hexene, 1.80 ± 0.08; 1-heptene, 2.06 ± 0.14; 3-methyl-1-butene, 1.39 ± 0.04; 3-methyl-1-pentene, 1.39 ± 0.03; 4-methyl-1-pentene, 1.52 ± 0.04; 3,3-dimethyl-1-butene, 1.54 ± 0.03; 3-methyl-1-hexene, 1.65 ± 0.08; 4-methyl-1-hexene, 1.86 ± 0.08; 5-methyl-1-hexene, 2.14 ± 0.08; 3,3-dimethyl-1-pentene, 1.44 ± 0.07; 3,4-dimethyl-1-pentene, 1.49 ± 0.10; and 4,4-dimethyl-1-pentene, 1.37 ± 0.06; where the indicated errors are two least-squares standard deviations and do not include uncertainties in the rate constant for the reference compound 1-butene. These rate constants increase along the series 1-butene < 1-pentene < 1-hexene < 1-heptene, and this is attributed to inductive effects. For a given carbon number, the rate constants depend on the position and degree of branching, and the observed trend of measured rate constants with position and degree of branching in the alkyl substituent group R correlates well with steric hindrance as calculated by McGillen et al. ( Phys. Chem. Chem. Phys. 2008 , 10 , 1757 ).