Conformational Analysis of Thiazole-5-Carboxylic Acid Using DFT/Td-DFT Methods

Abstract

In this work, structures of the conformers of the thiazole-5-carboxylic acid (T5CA) were studied using density functional theory (DFT) with B3LYP/6-311++G(d,p) level of approximation. From calculations of the potential energy distribution depending on the orientation of the carboxylic group (C-C-OH and O=C-OH) attached to the five-membered heterocyclic ring, four conformers were found at minimum energy. Considering that the relative energy in the most stable structure is zero. The relative energies of the other conformations were found to be about 0.14, 27.11, 29.84 kJ mol-1, respectively. It was found that the carboxylic acid group of the T5CA_3 and 4 were not planar, while T5CA_1 and T5CA_2 were planar. Stabilization and donoracceptor orbital interaction energies were calculated for all conformations and orbitals were plotted using natural bond orbital analysis (NBO) method. The excited state energies were calculated and graphed using Time-Dependent Density Functional Theory (TD-DFT) calculations. The singlet state energies were tabulated for all conformations and it was seen that the most stable form with the highest oscillator strength was at the second singlet state (S2). In addition, HOMO-LUMO energy gaps were calculated and electrostatic potential surface maps were drawn for all conformations.