Coexistence of Intra- and Intermolecular Hydrogen Bonds: Salicylic Acid and Salicylamide and Their Thiol Counterparts.

The ωB97-XD/6-311++G(d,p) calculations were carried out on dimers and monomers of salicylic acid and salicylamide as well as on their thiol counterparts; different conformations of these species were considered. The searches through the Cambridge Structural Database were performed to find related structures; thus the analysis of results of these searches is presented. Various approaches were applied to analyze inter- and intramolecular hydrogen bonds occurring in the above-mentioned species: natural bond orbital (NBO) method, symmetry-adapted perturbation theory (SAPT) approach, the quantum theory of atoms in molecules (QTAIM), and the electron localization function (ELF) method. The results of calculations indicate a slight mutual influence of inter- and intramolecular hydrogen bonds. However, the frequent occurrence of both interactions in crystal structures indicates the importance of their coexistence. The occurrence of intramolecular chalcogen bonds for trans conformations of species analyzed is also discussed.