Tautomerism Modulation in 4-Hydroxyquinoline through Incorporation of Nitro-group
Description
The present data showed the FID (for NMR spectra) and output (DFT-calculations) documents to study the tautomerism of the 4-hydroxyquinoline and their nitro-substituted 4-hydroxyquinolines. Six 4-hydroxyquinoline compounds and a 4-alcoxy-quinoline were analyzed from NMR spectroscopic study and DFT-calculations. Effect of solvent was analyzed.
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Theoretical Calculation. All DFT calculations were carried out at the Copernico Cluster of the computational center at Science Faculty (Universidad Central Venezuela). All theoretical calculations, in the gas phase, were performed using density functional theory (DFT) with the Gaussian quantum chemistry software.33 To achieve a balance between the computational cost and the accuracy of the calculations, M06-2X functional30 in combination with the def2TZVP basis set31. The geometries of the enol- and keto-tautomers of the hydroxyquinolines 1, 2, 3, 4 and 5 were optimized. Calculations were performed in the gas phase. All structures were optimized in the ground state without restrictions, using tight optimization criteria and an ultrafine grid in the computation of two-electron integrals and their derivatives. Optimization calculations were performed using the Berny algorithm and were successfully completed with the following parameters: maximum force, 0.000450; root-mean-square (RMS) force, 0.000300; maximum displacement, 0.001800; RMS displacement, 0.001200; predicted change in energy, −1.488276×10−8 Hartree for most of studied cases. The relative stability of the tautomers was presented as the difference between the total energies of the enol-tautomer against the keto-tautomer (ΔE=EE−EK). All calculation outputs can be found at the Section 2 of the Supporting Information Material. Further analysis to identify the occurrence of non-covalent interaction was performed on Multiwfn software, version 3.8,37 which allowed us to obtain the corresponding NCI (Non-covalent interaction) plots, RDG (Reduced Density Gradient) isosurfaces and ELF (Electron-localization Function) maps for the optimized structures for all studied benzylic compounds. NCI plots and RDG isosurfaces were generated on electron density isosurface of 0.05 a.u. Weak repulsive and weak attractive interactions are identified by green surface in RDG plots. NMR studies. The 1H-NMR spectra for the nitro-4-hydroxyquinolines 1, 2, 3, 4, 5 and 6 and O-alkylated derivative 7 were collected under various conditions. Sample stock solution (D2O, CD3OD, MeCN, DMSO-d6 and CDCl3) (10 mg in 0.5 mL) was prepared.