Investigation of intramolecular hydrogen bonding strength in dihydroxynaphthazarin: DFT and NBO studies

In order to study hydrogen bond strength changes in Dihydroxynaphthazarin in comparison with Naphthazarin, the full geometry optimization of these molecules have been performed by Density Functional Theory (DFT) method, at B3LYP theoretical level, using 6-311++G** basis set. Also, 1HNMR calculations were carried out by using GIAO methodand vibrational frequency calculations were performed for light and deuterated molecules.To support extracted results, NBO calculations(bond order, electron density, electron delocalization and steric effects) were also done at the same level of theory. In this study, we concluded that hydrogen bond strength in Dihydroxynaphthazarin is more than Naphthazarin when there is only one hydroxyl group in the vicinity of OH but when there is an OH group in the vicinity of carbonyl (even if there is another OH in the vicinity of hydroxyl groups) the related hydrogen bond strength is decreased.