Computational study on the molecular conformations of phenolic compounds

The study of the conformation of eight phenolic compounds (i.e. phenol, guaiacol, syringol, pyrocatechol, o-, m-, p-cresol and vanillin) was carried out using B3LYP (Becke, 3-parameter, Lee-Yan-Parr) method and cc-pVTZ (correlation consistent polarized polarisation Valence triple zêta) basis set. Potential energy surfaces were plotted in order to identify the minimum energy structures and the transition states. For the first time, structures of vanillin and syringol were completely determined. Moreover, our work also confirms that the most stable conformations of m-cresol and p-cresol are obtained when the methyl group presents a hydrogen atom at the perpendicular of the benzene ring. The possibility of intramolecular hydrogen bonding was also investigated. Guaiacol, pyrocatechol, syringol and vanillin present a structure stabilized by the presence of a moderate hydrogen bond. Finally, potential energy barriers and rotational potential functions were calculated. The comparison of the rotational potential parameters for each molecule highlights the presence of similarities specific to each substituent and their neighbours.