Reactivity of 5‐aminouracil derivatives towards peroxyl radicals

The reactivity of 5‐aminouracil derivatives in the model reaction of autoxidation of styrene initiated by 2,2′‐azobis(2‐methylpropionitrile) was studied. Alkyl substituents at the 6‐position of the uracil ring have a significant effect on the kinetic parameters of inhibition. The N‐H bond dissociation energy calculated at the M06‐2X/MG3S and G4 levels of the theory does not agree with the experimental values of the rate constants. The transition state was calculated at the M05/MG3S level of theory for 1,3‐dimethyl‐5‐aminouracil, 1,3,6‐trimethyl‐5‐aminouracil, 1,3‐dimethyl‐6‐ethyl‐5‐aminouracil, 1,3‐dimethyl‐6‐isopropyl‐5‐aminouracil and 3‐butyl‐6‐methyl‐5‐aminouracil. The enthalpy of the transition state is in agreement with the experimental data and it can be used to evaluate the reactivity of the 5‐aminouracil derivatives with peroxyl radicals.