Analysis of the relationship between electronic and spectral properties of conformer structures of 1,3,4-thiadiazole compounds by DFT and QTAIM methods

In this study, new 1,3,4-thiadiazole compounds were synthesised and characterised by FT-IR, 1H NMR, UV–vis spectroscopy and elemental analysis, Furthermore, the relationship between the electronic and spectral data of the 16 conformers of each compound was investigated by theoretical calculations; the theoretical data were compared with the experimental results. The B3LYP hybrid functional level with a 6-311++g(2d,2p) basis set was used to obtain the ground state geometries, frontier molecular orbital energies, band gap energies and chemical reactivity parameters, and the one was used to perform a spectral analysis of the compounds. Significant correlations were calculated between the minimum molecular energy and N–H and C=O vibrational frequencies and the NH proton chemical shifts of the conformers. The charge density on the nitrogen atom and the delocalisation index of the highly polar N–H covalent bond were investigated by quantum theory of atoms in molecules. The effect of conformer structure on the theoretical results and its role in interpreting the experimental data were presented, and it was theoretically shown that the activity degree of the non-aromatic electronegative atoms or groups of atoms in the intramolecular interaction was a very important factor in determining the electronic and spectral properties of each compound.