Experimental FT-IR and UV–Vis spectroscopic investigation of thiobenzamide and aminothiobenzamide derivatives supported by DFT calculations

Thiobenzamide (TBA), 2-aminothiobenzamide (2-ATBA), and 4-aminothiobenzamide (4-ATBA) were studied using both experimental and theoretical methods to learn more about their molecular properties. Experimental spectroscopic data were obtained using Fourier-transform infrared (FT-IR) and UV–Vis spectroscopy, while density functional theory (DFT) calculations performed at the B3LYP/6-311++G(d,p) level were used to support the structural analysis and spectral assignments. The optimized molecular geometries were consistent with the available experimental structural data. Moreover, the calculated vibrational frequencies, after applying appropriate scaling factors, showed good agreement with the experimental FT-IR spectra. The experimentally observed electronic absorption bands were also interpreted in terms of the predicted electronic transitions. The charge distribution, bonding features, and weak intramolecular interactions in the studied compounds were examined by molecular electrostatic potential surface (MEPS), atoms-in-molecules (AIM), and noncovalent interaction (NCI) analyses. The results show the important roles of the C = S and N–H groups on their electronic structures and mode of interaction. In addition, antimicrobial activities of TBA, 2-ATBA, and 4-ATBA were evaluated against the selected bacterial and fungal strains, providing preliminary information on their biological properties. To summarize, the experimental spectroscopic data and DFT-based data are consistent with each other, providing a coherent description of the structural, vibrational, and electronic properties of the thiobenzamide derivatives.