AbstractThe effect of various substituents on the rates of thermal decomposition of substituted bis‐(thenoyl) peroxides has been investigated. Nine unreported peroxides were prepared, including derivatives of 2‐ and 3‐thenoic acids. The thermal decomposition rates of these peroxides were examined, in the presence of styrene as a free radical scavenger. First order kinetics were observed in all cases studied. In general it was found that electron releasing substituents increase, while electron withdrawing groups decrease, the decomposition rate; the only exception being bis‐(5‐nitro‐3‐thenoyl) peroxide. Entropies and energies of activation were determined and found to be linearly related for the pero