Mecanistic investigation of formation reaction of some 4-oxo-1,3-thiazolidin-5-ylidene acetate derivatives

In this study, the molecular mechanism of N-[(2-benzylidenehydrazino)(imino)methyl]-N'-phenylthiourea and acetylenedicarboxylate compounds was investigated quantum mechanical by the density functional theory (DFT). Geometric optimizations for all fundamental steps of the reaction, including intermediates and transition states, were performed using the 6-31G basis set with the B3LYP hybrid functional, both in the gas phase and in the solvent phase (methanol). The calculations of the geometries, energy values and vibration frequencies were made with Gaussian 09 software using the same basis set. Considering the vibration frequencies for each structure, the most suitable structures with no imaginary frequency in the fundamental cases and a single imaginary frequency in the transitional states were determined. The IRC method was used to verify that the obtained transition states were effectively coupled to the desired structure. At the same time, energy profiles were obtained by obtaining free energy and enthalpy values for the reaction steps. The electronic, geometric and thermodynamic parameters obtained as a result of the calculations are shown in the tables. Apart from the activation energy values, the reaction mechanism was tried to be clarified by considering the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), bond lengths and angle values. Keywords: Acetylenedicarboxylate, DFT calculations, mechanism, transition state