10.6084/m9.figshare.6453236.v1 Huong Giang Thi Nguyen Huong Giang Thi Nguyen Vinh Ngoc Nguyen Vinh Ngoc Nguyen Fadhil R Kamounah Fadhil R Kamounah Poul Erik Hansen Poul Erik Hansen Dataset for: Structure of a new Usnic acid derivative from a deacylating Mannich reaction. NMR studies supported by theoretical calculations of chemical shifts. Wiley 2018 DFT calculations deuterium isotope effects on chemical shifts Mannich reaction Usnic acid isotope effects on chemical shifts deacylation NMR Spectroscopy Structural Biology 2018-07-03 03:05:09 Dataset https://wiley.figshare.com/articles/dataset/Dataset_for_Structure_of_a_new_Usnic_acid_derivative_from_a_deacylating_Mannich_reaction_NMR_studies_supported_by_theoretical_calculations_of_chemical_shifts_/6453236 In a conventional Mannich reaction using piperidine, hydroxypiperidines, morpholine and N-methylpiperazine with usnic acid a deacetylation was observed resulting in a substitution at C-2, loss of an acetyl group and a Mannich base with a stabilized enol. The enol has a hydrogen bond to the nitrogen of the secondary amine. The structure was investigated by NMR and deuterium isotope effects on 13C chemical shifts as well as with DFT calculations to study the changed hydrogen bond pattern. It was found that the hydrogen bond involving the OH-9 group in chloroform forms a strong hydrogen bond than in usnic acid itself and that this hydrogen bond becomes even stronger in the more polar solvent, dimethylsulfoxide. Tautomerism was observed in the Mannich base as demonstrated by deuterium isotope effects on chemical shifts. The position of the tautomeric equilibrium depends on the solvent and the position of the equilibrium governs the strength of the OH-9...O=C hydrogen bond.