Experimental and theoretical quantum chemical investigations of 8-hydroxy-5-nitroquinoline

The FT-IR and FT–Raman spectra of 8-hydroxy-5-nitroquinoline have been recorded in the regions 4000–400 and 4000–100 cm−1, respectively. The spectra were interpreted in terms of fundamentals modes, combination and overtone bands. The normal coordinate analysis was carried out to confirm the precision of the assignments. The structure of the compound was optimised and the structural characteristics were determined by density functional theory (DFT) using B3LYP method with 6-31G∗∗, 6-311++G∗∗ and cc-pVDZ basis sets. The vibrational frequencies were calculated in all these methods and were compared with the experimental frequencies which yield good agreement between observed and calculated frequencies. The infrared and Raman spectra were also predicted from the calculated intensities. 1H and 13C NMR spectra were recorded and 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were calculated using the gauge independent atomic orbital (GIAO) method. UV–Visible spectrum of the compound was recorded and the electronic properties HOMO and LUMO energies were measured by time-dependent TD–DFT approach. The influences of the nitro and hydroxy groups on the skeletal modes and on the proton chemical shifts have been investigated.

Graphical abstractThe FT-IR, FT-Raman, 1H, 13C NMR and UV–Visible spectral measurements of 8-hydroxy-5-nitroquinoline and complete assignments of the observed spectra have been proposed. HF/DFT calculations have been performed and the structural parameters of the compounds were determined from the optimised geometry with 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets and giving energies, harmonic vibrational frequencies, depolarisation ratios, IR and Raman intensities. The geometric parameters, harmonic vibrational frequencies and chemical shifts were compared with the experimental data of the molecules. The influences of hydroxyl and nitro groups on the skeletal modes and proton chemical shifts have been investigated. A detailed natural bond orbital analysis was carried out.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► FTIR, FT-Raman, FT-NMR and UV–Visible spectral investigations of 8-hydroxy-5-nitroquinoline were carried out. ► Energy, structural, thermodynamical, vibrational and electronic characteristics were determined. ► 1H and 13C NMR spectra and chemical shifts were measured by GIAO method. ► The electronic properties by TD–DFT approach and NBO analysis were carried out. ► Effect of hydroxy and nitro groups on the quinoline ring parameters have been analysed.