A computational study of the structure, aromaticity and enthalpy of formation of UVA filter 4-tert-butyl-4′-methoxydibenzoylmethane

In this study we have performed a density functional theory (DFT) study of the molecular structure and energetics of the enol and keto tautomers of UVA filter 4-tert-butyl-4′-methoxydibenzoylmethane (BMDBM) and for comparison and validation purposes a similar study has been carried out for the parent molecule: dibenzoylmethane (DBM). The molecular structure of the enol and keto tautomers were obtained at the B3LYP/6-311++G(d,p) level. The enol forms were found to have a strong intramolecular resonance assisted hydrogen bond that accounts for the greater energetic stability of the enol relative to the keto form. The aromatic character of the six-membered enol rings has been analyzed by calculation of Nucleus Independent Chemical Shifts (NICS). The standard molar enthalpy of formation in the gas phase of BMDBM was derived from appropriately chosen reactions.