A computational evidence of the intermolecular/intramolecular hydrogen bonding in salicylsalicylic acid: chemical shielding tensors and AIM analysis

A computational study has been performed at the B3LYP/6-31++G** level to evidence hydrogen bonding interactions in the real crystalline structures of salicylsalicylic acid (salsalate) via chemical shielding tensors at the O-17 nuclei. Real crystalline structure of salsalate reveals two conformers (major and minor). One molecule (monomer), two molecules (dimer), and four molecules (cluster) of conformers of salsalate are modeled by accessible crystal coordinates. The chemical shielding tensors are calculated for three models of both configurations indicating the effect of hydrogen bonding interactions on the NMR parameters. The evaluated NMR parameters of O-17 nuclei of COOH group are significantly alternated from monomer to the target molecule in the dimer due to the contribution in the intermolecular (HO)-C=O center dot center dot center dot H-O-(CO) hydrogen bonds, whereas alternation is insignificant from dimer to the target molecule in the cluster because the number and type of hydrogen bonds do not change. On the other hand, the change in evaluated NMR parameters of O-17 nuclei of (C=)O and O(-H) from the monomer to the target molecule in the dimer and cluster is almost negligible due to the contribution in the intramolecular C=O center dot center dot center dot H-O hydrogen bonds in two conformers. Atoms in molecules (AIM) analysis confirms the presence of hydrogen bondings and vindicates the calculated chemical shielding trends. [GRAPHICS] .