Conformational analyses of all possible cis-enol forms and their molecular structures for benzoylacetone (BA), dibenzoylmethane (DBM) and 1-benzoyl-3,3-dimethane-2-buthanone (BDMB) have been investigated by means of density functional theory (DFT) calculations at B3LYP/6-311++G** level. The results are compared with those of acetylacetone (AA) and 5,5-dimethyl hexane-2,4-dione (DMHD). Since the energy differences between stable cis-enol conformers are negligible, coexisting of stable cis-enol conformers in comparable proportions in the sample is suggested. The fully optimized geometrical parameters and their averaged values for DMHD, BDMB, DBM, BA, and AA indicate that the intramolecular hydrogen bond strength increases by substitution of the CH3 groups by Ph groups. This is in good agreement with the experimental 1HNMR results.

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