A new series of Schiff bases derived from sulfa drugs and indole-3-carboxaldehyde: Synthesis, characterization, spectral and DFT computational studies

A new series of Schiff bases were synthesized for the first time by the condensation of indole-3-carboxaldehyde with various sulfa drugs including sulfanilamide, sulfapyridine, sulfadiazine, sulfamerazine, sulfamethoxazole, sulfamethoxypyridazine and sulfacetamide sodium in ethanol (1:1). The structure of Schiff bases were experimentally characterized by using IR, 1H NMR, 13C NMR and mass spectroscopic methods. The structural and electronic properties of the studied molecules were investigated theoretically by performing density functional theory (DFT) to access reliable results to the experimental values. The molecular geometry, the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) and Mulliken atomic charges of the studied molecules have been calculated at the B3LYP method and standard 6-31 + G(d,p) basis set starting from optimized geometry. The theoretical 13C chemical shift results were also calculated using the gauge independent atomic orbital (GIAO) approach and their respective linear correlations were obtained. The comparison of the results indicates that B3LYP/6-31 + G(d,p) yields good agreement with the observed chemical shifts.