The gas-phase reaction of ozone with eight 1,2-disubstituted alkenes has been investigated at ambient temperature (T = 286–296 K) and p = 1 atm. of air. The reaction rate constants, in units of 10⁻¹⁸ cm³ molecule⁻¹s⁻¹, are 144 ± 17 for cis-3-hexene, 157 ± 25 for trans-3-hexene, 89.8 ± 9.7 for cis-4-octene, 131 ± 15 for trans-4-octene, 114 ± 13 for cis-5-decene, ≥ 130 for trans-5-decene, 38.3 ± 5.0 for trans-2.5-dimethyl-3-hexene, and 40.3 ± 6.7 for trans-2.2-dimethyl-3-hexene. Substituent effects on alkene reactivity are examined. Cis-1,2-disubstituted alkenes are less reactive than the corresponding trans isomers. The 1,2-disubstituted alkenes that bear bulky substituents (substitution at the 3-carbon) are ca. 3 times less reactive than the corresponding n-alkyl substituted compounds. The atmospheric persistence of 1,2-disubstituted alkenes is briefly discussed. © 1996 John Wiley & Sons, Inc.