Synthesis, isomerization, and DFT studies of five-membered heterocyclic ketoximes

Abstract

A homologous series of five-membered heterocyclic ketoximes is synthesized by condensation reactions of 2-acetylpyrrole, 2-acetylthiophene, and 2-acetylfuran with hydroxylamine hydrochloride. These compounds were fully characterized by X-ray single-crystal diffraction, elemental analysis, 1H NMR, IR, UV-Vis, and fluorescence spectra. Interesting isomerization phenomena are observed for these heterocyclic ketoximes by different characterization methods. By means of 1H NMR and X-ray single-crystal diffraction, it was found that 2-acetylpyrrole oxime (1) exists as the Z-type geometric isomer, 2-acetylfuran oxime (3) exists as the E-isomer, while 2-acetylthiophene oxime (2) is identified as a mixture of Z- and E-isomers. To study the above phenomena further, quantum chemical calculations of total energy, dipole moment, EHOMO, ELUMO, and other parameters of each heterocyclic ketoxime were carried out by Density functional theory (DFT). The theoretical calculations were in good accordance with the experimental spectroscopic results.