In this work, the chemical reactivity of isoxaflutole (ISOX) and diketonitrile (DKN) was analyzed at the X/6-311++G(2d,2p) (where X = = B3LYP, M06, M06L and ?B97XD) level of theory, in the gas and aqueous phases. The results indicate that DKN, the active metabolite of ISOX, is more stable than isoxaflutole in both phases. ISOX is susceptible to electrophilic and free radical reactions through the isoxazole ring; while the carbonyl group is attacked by nucleophiles. For DKN nucleophilic and free radical attacks are expected on the aromatic ring, while electrophilic attacks are favored on the oxygen atom of the carbonyl groups. The results suggest that the cleavage of the N?O bond in the isoxazole ring is possible through electrophilic and free radical attacks, while electrophilic and free radical attacks will favor substitutions on the carbonyl groups of DKN.