Structural, vibrational, electronic investigations and quantum chemical studies of 2-amino-4-methoxybenzothiazole

Extensive vibrational investigations of 2-amino-4-methoxybenzothiazole have been carried out with FTIR and FT-Raman spectral techniques. The electronic structure of the molecule has been analysed by UV–Visible and NMR spectroscopies. The DFT studies were carried out with B3LYP and HF methods utilising 6-31G(d,p), 6-311++G(d,p) and cc-pVDZ basis sets to determine the structural, thermodynamical, vibrational, electronic characteristics of the compound and also to understand the electronic and steric influence of the methoxy amino groups on the skeletal frequencies. The mixing of the fundamental modes was determined with the help of total energy distribution (TED). The energies of the frontier molecular orbitals have also been determined. The kinetic and thermodynamic stability and chemical hardness of the molecule have been determined. Complete NBO analysis was also carried out to find out the intramolecular electronic interactions and their stabilisation energy. 1H and 13C NMR chemical shifts and the electronic transitions of the molecule are also discussed.

Graphical abstractThe FT-IR, FT-Raman, 1H, 13C NMR and UV–Visible spectral measurements of 2-amino-4-methoxybenzothiazole and complete analysis 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 amino and methoxy 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 and FT-Raman investigations of 2-amino-4-methoxybenzothiazole were carried out. ► The nN→πNC∗ interaction is 10.58 kJ/mol more stabilised than nS→πNC∗. ► The strong absorption peak observed at 263.2 nm is caused by the π  π* transitions. ► 1H and 13C NMR chemical shifts and the electronic transitions of the molecule were discussed. ► The amino (5.83 ppm) and methoxy (3.94 ppm) group protons are under high magnetic shielding.