Ab initio study on transition states of formohydroxamic acid tautomerization in the presence of water molecules

Keto-iminol transformation of formohydroxamic acid in the presence of water molecules is investigated using ab initio quantum mechanics calculations. Calculations revealed that the proton transfer energy barriers are significantly lowered in the presence of water molecules. The proton transfer in Z-keto form occurs via a pathway involving two transition states and a charge separated intermediate. The proton transfer in E-keto tautomer occurs via a single transition state. A third pathway, which is not feasible in the absence of water, becomes feasible when there are hydrogen bonded water molecules. The stability order of formohydroxamic acid tautomers was found to be E-keto > Z-keto > Z-iminol > E-iminol and remains the same even after hydrogen bonded to water.