Estudo teórico do guaiacol e seus dímeros: estrutura eletrônicae vibracional

Abstract

The electronic, structural, vibrational, and topological properties of different orto-methoxyphenol (guaiacol) conformers and dimers have been investigated by quantum chemistry methods. DFT methods corrected by dispersion and DLPNO- CCSD(T) calculations were employed. As possible, the theoretical outcomes were compared with vibrational spectroscopy measurements in the infrared region. Studying this compound is pivotal to improving our knowledge about miscibility in different solvents and extraction processes conducted in the chemical industry. The formation of an intramolecular hydrogen bond and the vibrational spectra of the isolated guaiacol were investigated, as the dimer formation with different solvents and how the guaiacol-solvent interactions affect the vibrational spectra were also studied. The following molecules were considered as solvents: orto, meta, para-cresol, propanone, acetic acid, water, and cyclohexane. For a better understanding of the hydrogen bond formation, the QTAIM method was used, and the study of the OH stretch was conducted assuming the harmonic approach and including anharmonic corrections. According to the QTAIM outcomes, the expected intramolecular hydrogen bond between the phenolic OH group and the methoxy oxygen is not formed. However, the results indicate the formation of a weak hydrogen interaction of the CH-- -O type in the guaiacol structure. Although, the vibrational spectra and the energy difference between conformers indicate the expected intramolecular hydrogen bond. It is verified that the guaiacol molecule is a system where the QTAIM method fails to predict an intramolecular hydrogen bond formation. The guaiacol-solvent interaction energy was evaluated, indicating that the guaiacol has an affinity for solvent candidates. However, the pairwise interaction calculated according to the approach of the present work was not adequate to reproduce the experimental miscibility pattern. The inclusion of anharmonic corrections in the frequency calculations led to a good agreement between the experimental and theoretical outcomes, indicating that the studied species should be present in the condensed phase.