Abstract
Rate coefficients and/or mechanistic information are provided for the reaction of Cl‐atoms with a number of unsaturated species, including isoprene, methacrolein (MACR), methyl vinyl ketone (MVK), 1,3‐butadiene, trans‐2‐butene, and 1‐butene. The following Cl‐atom rate coefficients were obtained at 298 K near 1 atm total pressure: k(isoprene) = (4.3 ± 0.6) × 10^−10^cm^3^ molecule^−1^ s^−1^ (independent of pressure from 6.2 to 760 Torr); k(MVK) = (2.2 ± 0.3) × 10^−10^ cm^3^ molecule^−1^ s^−1^; k(MACR) = (2.4 ± 0.3) × 10^−10^ cm^3^ molecule^−1^ s^−1^; k(trans‐2‐butene) = (4.0 ± 0.5) × 10^−10^ cm^3^ molecule^−1^ s^−1^; k(1‐butene) = (3.0 ± 0.4) × 10^−10^ cm^3^ molecule^−1^ s^−1^. Products observed in the Cl‐atom‐initiated oxidation of the unsaturated species at 298 K in 1 atm air are as follows (with % molar yields in parentheses): CH~2~O (9.5 ± 1.0%), HCOCl (5.1 ± 0.7%), and 1‐chloro‐3‐methyl‐3‐buten‐2‐one (CMBO, not quantified) from isoprene; chloroacetaldehyde (75 ± 8%), CO~2~ (58 ± 5%), CH~2~O (47 ± 7%), CH~3~OH (8%), HCOCl (7 ± 1%), and peracetic acid (6%) from MVK; CO (52 ± 4%), chloroacetone (42 ± 5%), CO~2~ (23 ± 2%), CH~2~O (18 ± 2%), and HCOCl (5%) from MACR; CH~2~O (7 ± 1%), HCOCl (3%), acrolein (≈3%), and 4‐chlorocrotonaldehyde (CCA, not quantified) from 1,3‐butadiene; CH~3~CHO (22 ± 3%), CO~2~ (13 ± 2%), 3‐chloro‐2‐butanone (13 ± 4%), CH~2~O (7.6 ± 1.1%), and CH~3~OH (1.8 ± 0.6%) from trans‐2‐butene; and chloroacetaldehyde (20 ± 3%), CH~2~O (7 ± 1%), CO~2~ (4 ± 1%), and HCOCl (4 ± 1%) from 1‐butene. Product yields from both trans‐2‐butene and 1‐butene were found to be O~2~‐dependent. In the case of trans‐2‐butene, the observed O~2~‐dependence is the result of a competition between unimolecular decomposition of the CH~3~CH(Cl)CH(O•)CH~3~ radical and its reaction with O~2~, with k~decomp~/k~O2~ = (1.6 ± 0.4) × 10^19^ molecule cm^−3^. The activation energy for decomposition is estimated at 11.5 ± 1.5 kcal mol^−1^. The variation of the product yields with O~2~ in the case of 1‐butene results from similar competitive reaction pathways for the two β‐chlorobutoxy radicals involved in the oxidation, ClCH~2~CH(O•)CH~2~CH~3~ and •OCH~2~CHClCH~2~CH~3~. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 334–353, 2003