Theoretical studies of the equilibria between two enolic forms of asymmetric beta-diketones

O-17 NMR chemical shifts of two frozen enols in hydrogen tautomerizations f or asymmetric B-diketones were calculated at the Hartree-Fock and density f unctional B3LYP levels of theory using various basis sets. From the theoret ical O-17 chemical shifts of frozen enols, the equilibrium constants for th e enol-enol equilibria were estimated and used for comparison with previous experimental results based on model shifts for the pure enol forms. The re sults show that our theoretical method can complement some inadequacies in the experimental NMR techniques in evaluating equilibrium constants of syst ems undergoing rapid dynamic equilibrium. Copyright (C) 2001 John Wiley & S ons, Ltd.