Theoretical and spectroscopic study of vanillic acid

Molecular dynamics simulations and density functional calculations are carried out to investigate the conformational space and electronic, magnetic and vibrational properties of vanillic acid. Results indicate that vanillic acid presents four stable conformers, but two of them lie very high in energy to make important contributions to properties at room temperature. H-1 and C-13 chemical shifts, acidity constants and electronic transition energies are calculated for the lower-energy conformers and compared with experimental data when available. Harmonic vibrational frequencies are also calculated for three different dimers of vanillic acid and compared with experimental IR spectrum. Both the electronic and IR spectra are recorded and completely assigned with the help of theoretical results. (C) 2008 Elsevier B.V. All rights reserved.