Propylene was ozonized in isobutane, chlorodifluoromethane, and methyl chloride solvents. Propylene ozonide, ethylene ozonide, and 2-butene ozonide (cis and trans isomers) were obtained in ratios of about 82:16:2. The amount of butene ozonide increased while that of ethylene ozonide usually decreased for reactions in the presence of added acetaldehyde. The cis-trans stereochemistry of the butene cross ozonide from propylene was studied at various conditions. Usually the cis isomer was preferentially formed, but addition of acetaldehyde could alter this. The cis-/trans-butene ozonide ratio was 67/33 when formed from cis- or trans-2-butene in CHC1F2 and 50/50 as a cross ozonide from trans-2-pentene. The kinetic secondary isotope effects upon ozonolysis of propene-2-d1 (kH/kD = 0.88 (6)) and propene-1-d1 (0.88 (8)) were evaluated. These results are discussed with reference to the Criegee mechanism of ozonolysis. © 1983, American Chemical Society. All rights reserved.