AbstractGas‐phase rate constants for the reaction of NO2with 16 conjugated olefins were determined at room temperature by either conventional methods for bimolecular processes or by competitive reactions. It was found that the rate constants for conjugated olefins were larger than those for simple mono‐olefins by factors of 103–104. Temperature dependence studies reveal that the difference in the rate constants for the two types of reactions can primarily be attributed to differences in their activation energies:k1,3‐cyclohexadiene= 5.8 × 10−14exp[−(6.1 ± 1.6)/RT] cm3molecule−1s−1;kcis‐2‐butene= 4.68 × 10−14exp(−11.2/RT) cm3molecule−1s−1[2]. A linear free energy relationship between the reactions of OH and NO2with con