Experimental (X-ray Diffraction, UV–Vis Spectroscopy) and DFT Studies of 1-Ethyl-3-methylquinoxaline-2-thione

Abstract

In this paper, we present the experimental and theoretical investigation of 1-ethyl-3-methylquinoxaline-2-thione, molecule exhibiting an important biological activity. We used X-ray diffraction, UV-visible absorption spectroscopy and DFT calculations with 6-31G(d,p) basis sets. According to the results, the compound crystallizes in the monoclinic system, P21/c with eight molecules per unit cell (Z = 8, Z ' = 2) and with the lattice parameters (a = 7.7882(8) A, b = 15.964(2) A, c = 16.519(2) A, α = 90°, β = 94.413(11)°, γ = 90°), in which the two fused-rings adopt a planar geometry, and assumes a dihedral angle with the ethyl group, presenting the most stable conformation. UV–Vis absorption spectroscopic properties of 1-ethyl-3-methylquinoxaline-2-thione showed a redshift when the solvent polarity increases from ethanol to DMSO. Detailed analysis of intra and intermolecular interactions as such H-bonding, π–π stacking, electronic transitions, HOMO–LUMO patterns, molecular electrostatic potential maps and Mulliken charges distribution was carried out in order to investigate charge transfer within the molecule for the needs of biomedical applications.