AN AM1 AND PM3 STUDY OF HEXAFLUOROACETYLACETONE

The AM1 and PM3 methods with the inclusion of a limited configuration interaction (CI) approach were used to study the stabilities of the ta utomers of hexafluoroacetylacetone (HFAA). It was found that the most stable tautomer is the hydrogen bonded cyclic asymmetric enol form, th e energy of which is lower than that of any keto tautomer by at least 2.5 kcal mol-1 with the AM 1 model and 0.9 kcal mol-1 with the PM 3 mo del. It was shown that HFAA should be an O-H acid. The intramolecular hydrogen bond energy is 4.5 kcal mol-1 with the AM 1 model and 4.8 kca l mol-1 with the PM3 model. It was shown that proton transfer from one oxygen atom to the other is controlled by the double minimum potentia l curve and the correspondig energy barrier height is 24.1 kcal mol-1 with the AMI model and 27.4 kcal mol-1 with the PM3 model.