Experimental and theoretical investigation of the synthetic characterization spectroscopic properties of some new Schiff base molecules

Schiff bases are a group of chemical compounds that have attracted attention in fields such as chemistry, biology, pharmacy and medicine, and they are obtained as a result of reaction with primary amines in the presence of aldehydes or ketones. The first step of the Schiff base compound synthesis, which takes place in two steps, is the condensation of the carbonyl carbon and the primary amine, and the second step is the formation of the imine compound over this intermediate product formed in the first step. In this study, firstly, 2-Acetonaptanone, 1-(2-Bromophenyl)ethanone, 1-(3,5-di-tert-butyl-2-hydroxyphenyl)ethan-1-one compounds were mixed with isophorondiamine compound in ethanol solution in the presence of weak acid catalyst. Three new Schiff base ligands were synthesized from the reaction. The main aim of the study is to experimentally synthesize new compounds whose synthesis is predicted, and to accurately illuminate the structures of these compounds, to compare experimental and theoretical spectroscopic properties of molecules, as well as to examine some physicochemical properties such as electronic, chemical potential, bond length, bond angles, electronegativity. The structures of the obtained molecules were elucidated by using TLC and IR, NMR, UV-Vis region spectroscopy techniques. While the transition from carbonyl compound to Schiff base can be observed with thin layer chromatography (TLC) at certain intervals during the reaction, in IR spectrophotometer, one of the most distinctive features is that the specific 1680 ~ 1720 cm-1 carbonyl band belonging to the (C=O) group in carbonyl compounds is replaced by the imine group (C=N) 1550 ~ 1650 cm-1 band, and the band belonging to the carbonyl group disappears. In NMR and UV-Vis region methods, distinctive features of the imine group based on the literature can be detected. After the synthesis studies and experimental analyzes were completed, the theoretical calculations of the synthesized molecules were started as the second step, for these calculations, using the Gaussian 09 package program Density Functional Theorem (DFT), the 6-311++G (d, p) base set was selected with the B3LYP method, which is known to be the most suitable for organic molecules in the literature. The spin multiplicity of the synthesized molecules was determined as singlet by taking the total charge to zero and other theoretical calculations were carried out on these structures by optimizing the stable molecules. Some physicochemical properties of Schiff bases such as bond lengths, bond angles, electrostatic potential, HOMO-LUMO values, natural bond orbital atomic charges and chemical parameters were calculated by IR, 1H-NMR, 13C-NMR, UV-Vis region spectroscopic methods and compared with experimental data.