A theoretical study on the solvent-assisted proton transfer in 5-hydroxyisoxazole

The process of the ground-state solvent-assisted (water, ammonia and methanol) proton transfer between 5-hydroxyisoxazole (HIO) and 5-ketoisoxazole (KIO) is studied using density functional theory of quantum chemistry method at B3LYP/6-31G* and B3LYP/6-31G** level. The calculated results show that the enol tautomers of all the clusters is more stable with 1.75 to 2.84 kcal mol−1 than the keto tautomers, and the barriers of intermolecular proton transfer in the clusters are low, ranging from 6.26 to 9.60 kcal mol−1 at B3LYP/6-31G** level. The calculations at B3LYP/6-31G* level underestimate the stability of enol tautomers and the barrier of proton transfer.