Theoretical studies on tautomerism of benzoylcyclohexane-1,3-dione and its derivatives

In the present paper, geometry optimizations were performed at HF/6-31G* level for all of the possible tautomers of benzoylcyclohexanedione. For one triketone and two cis-endocyclic double bond enol tautomers that have lowest energies, extensive calculations were performed. The effect of calculation method and the size of the basis set on the relative stability of the tautomers were investigated. In addition, the tautomeric equilibrium constants and the energy barrier of the benzoylcyclohexane-1,3-diones were calculated. The solvent effect was fully considered when calculating the equilibrium constants and the results were analyzed by comparing with the experimental results. Finally, calculations were performed on representative 2-substituted benzoylcyclohexane-1,3-dione derivatives. It appears that the free energy of tautomerization and their HPPD inhibitive activity correlated closely.