Ab initio and DFT Calculation of Conformational Properties and Thermodynamic Properties of Sterically Congested 5-(4-Bromophenyl)-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. Experimental measurements andtheoretical calculations on vibrational frequencies become one of the key factors in themolecular structure correlations design. For a proper understanding of IR and Raman spectra,a reliable assignment of all vibrational bands is essential. For this purpose, the quantumchemical methods, ranging from semi-empirical to DFT approaches, are invaluable tools[2,3], On the other hand, DFT methods, particularly hybrid functional methods, have evolvedto a powerful quantum chemical tool for the determination of the electronic structure ofmolecules. Among these, the B3LYP combination is the most used since it proved its abilityin reproducing various molecular properties, including vibrational spectra. In connection withour recent interest to multicomponent reactions, we report synthesis and FT-IR studies of 5-(4-Bromophenyl)-N -(trichloroacetyl)-1,3,4-oxadiazole-2-carboxamide. The B3LYP/HFcalculations for computation of FT-IR spectra have been carried out for the title compoundsat the 6-31G* and 6-311++G** basis set levels. Predicted vibrational frequencies have beenassigned and compared with experimental FT-IR spectra and they are supported each other.