AbstractRate constants for the gas phase reactions of O3 and OH radicals with 1,3‐cycloheptadiene, 1,3,5‐cycloheptatriene, and cis‐ and trans‐1,3,5‐hexatriene and also of O3 with cis‐2,trans‐4‐hexadiene and trans ‐2,trans ‐4‐hexadiene have been determined at 294 ± 2 K. The rate constants determined for reaction with O3 were (in cm3 molecule‐1s−1 units): 1,3‐cycloheptadiene, (1.56 ± 0.21) × 10‐16; 1,3,5‐cycloheptatriene, (5.39 ± 0.78) × 10−17; 1,3,5‐hexatriene, (2.62 ± 0.34) × 10−17; cis−2,trans‐4‐hexadiene, (3.14 ± 0.34) × 10−16; and trans −2, trans ‐4‐hexadiene, (3.74 ± 0.61) × 10−16; with the cis‐ and trans‐1,3,5‐hexatriene isomers reacting with essentially identical rate constants. The rate constants determined for reaction with OH radicals were (in cm3 molecule−1 s−1 units): 1,3‐cycloheptadiene, (1.31 ± 0.04) × 10−10; 1,3,5‐cycloheptatriene, (9.12 × 0.23) × 10−11; cis‐1,3,5‐hexatriene, (1.04 ± 0.07) × 10−10; and trans 1,3,5‐hexatriene, (1.04 ± 0.17) × 10−10. These data, which are the first reported values for these di‐ and tri‐alkenes, are discussed in the context of previously determined O3 and OH radical rate constants for alkenes and cycloalkenes.