Illumination of the structures of some sulfonamide compounds with biological activity by spectroscopic methods and investigation of their physical properties by DFT method

Sulfonamides are synthetic antibacterial compounds and broad-spectrum drugs that are active against various types of bacteria, generally gram-positive and gram-negative. With the widespread use of sulfonamides immediately after their discovery, a significant reduction in diseases caused by bacteria has been observed. In this study, the chemical structure of 2,4-dihydroxybenzaldehyde Sulfisoxazole Schiff base (S2M-S3) was tried to be elucidated by 1H-NMR, 13C-NMR and FT-IR spectroscopic methods. As a result of the vibration frequencies, 1H-NMR and 13C-NMR calculations, it was seen that the theoretical values were compatible with the experimental values. In addition, HOMO-LUMO molecular orbital energies, nonlinear optical properties such as polarizability, hyper polarizability (NLO) and molecular electrostatic potential (MESP) of S2M-S3, Cu (S2M-S3)2 and Pd (S2M-S3)2 compounds were investigated. As a result of the geometry optimization calculation, S=O and S-N bond lengths were obtained slightly longer than the results found in previous studies. The N-H bond length is in agreement with previous studies. In the calculations, the energy band gap between the HOMO and LUMO orbitals of the S2M-S3 compound was 4.09 eV and the initial static hyperpolarizability was 27677.7×10-33 esu. Keywords: FT-IR, NMR, NLO, DFT, HOMO, LUMO