FT-IR Spectra and DFT calculations on sterically congested 5-(4-Chlorophenyl)- N -(trichloroacetyl)-1,3,4-oxadiazole-2-carboxamide

In the past decade, IR spectroscopy have become important techniques for obtaininginformation on chemical structures and are applied in virtually all branches of chemistry.Vibrational spectroscopy is used extensively in organic chemistry for the identification offunctional groups of organic compounds as well as for studies on molecular conformation,reaction kinetics, etc [1]. Density functional theory (DFT) has become a major tool in themethodological arsenal of computational organic chemists. DFTmethods are increasinglyapplied to representative pharmacological compounds aiming to elucidate their molecularstructures, electronic properties and bonds, the establishment of electronic and structuralfactors of selected reactions and their mechanisms. For this purpose, the quantum chemicalmethods, ranging from semi-empirical to DFT approaches, are invaluable tools [2-3], eachmethod having its own advantages. The semiempirical calculations provide very fast, and incertain circumstances fairly good theoretical results, being applicable to large molecularsystems. HF methods are able to give good results provided a reasonable basis set and anappropriate correlation treatment is taken into account. On the other hand, DFT methods,particularly hybrid functional methods, have evolved to a powerful quantum chemical toolfor the determination of the electronic structure of molecules. Among these, the B3LYPcombination is the most used since it proved its ability in reproducing various molecularproperties, including vibrational spectra. In connection with our recent interest tomulticomponent reactions, we report synthesis and FT-IR studies of 5-(4-Chlorophenyl)-N -(trichloroacetyl)-1,3,4-oxadiazole-2-carboxamide. The B3LYP/HF calculations forcomputation of FT-IR spectra have been carried out for the title compounds at the 6-31G*and 6-311++G** basis set levels. Predicted vibrational frequencies have been assigned andcompared with experimental FT-IR spectra and they are supported each other.