Intramolecular OHO bonding in dibenzoylmethane: symmetry and spectral manifestations

Abstract

Although both experimentalists and theoreticians agree that dibenzoylmethane exists in the enol form, there are different opinions concerning symmetry of the OHO fragment. Consequently, assignment of its vibrational spectra has been incomplete. In this contribution we computed Gibbs free energies with the G4MP2 method. Multi-dimensional potential energy surfaces obtained at M06-2X/cc-pVTZ level enabled vibrational analysis and comparison with available experimental data. Our results revealed presence of two conformers in the gas phase at room temperature, the asymmetric structure (with O–H stretching frequency around 2400 cm⁻¹ and very low infrared intensity), and the symmetric conformer (with O⋯H⋯O asymmetric stretching band located around 500 cm⁻¹). Characterization of hydrogen bonds was performed with quantum theory of atoms in molecules (QTAIM), which showed that O–H⋯O group represents a typical hydrogen bond, whereas hydrogen bonds in the O⋯H⋯O fragment have substantial covalent character.