Synthesis Characterization and DFT Calculations of 2,5-Substituted Thiophene Derivatives

Thiophene-2,5-dicarbonyl dichloride was treated with pyrazole and 3-methylpyrazole (3-MePz) in the presence of trimethylamine. Under normal conditions at room temperature, thiophene-2,5-diylbis((1H-pyrazol-1-yl)methanone) (1) and thiophene-2,5-diylbis((3-methyl-1H-pyrazol-1-yl)methanone) (2) were afforded, respectively. Structure of compounds was deduced from the characteristic H-1 and C-13-NMR data set. The structure of compound 2 was also confirmed by X-ray diffraction. Selected parameters of compound 1 and structural parameters of compound 2 were calculated by DFT using B3LYP/G-311 level of theory. The calculated data (bond lengths and angles) were found in close agreement with the experimental data. The compound 2 in solid state has planar structure, the free rotation of 3-methylpyrazolyl group has probably been restricted by some sort of intermolecular interactions. In contrast the gas phase optimized structure shows that 3-MePz rings stabilize themselves at maximum distance from each other. Pyrazolyl and 3-methylpyrazolyl substituted compounds derived from thiophene-2,5-dicarbonyl dichloride were obtained. The X-ray structure of 3-methylpyrazolyl substituted derivative was established, the solid state data was also calculated by DFT. The experimental structure shows high degree of planarity while optimized structure allows free rotation of the substituents.