Molecular structural, IR and NMR spectroscopic studies on the four isomers of thiotriazinone by DFT and HF calculations

Abstract

One of the isomers of thiotriazinone, 6-hydroxy-2-methyl-3-thioxo-2H-1,2,4-triazin-5-one, was characterized by single-crystal X-ray diffraction. The compound crystallizes in the monoclinic space group P2(1)/ c with a = 9.5837(19) Å, b = 5.7006(11) Å, c = 15.065(4) Å, α = 90°, β = 128.540(19)° and γ = 90°. The molecular geometries and vibrational frequencies of the four isomers of thiotriazinone in the ground state have been calculated using the density functional theory (DFT) and Hartree–Fock (HF) methods with 6-311++G(d,p) basis set, and compared with the experimental data. Gauge-including atomic orbital (GIAO) 13C and 1H NMR chemical shift values were calculated by DFT/6-311++G(2d,2p) and HF/6-311++G(2d,2p) methods, and compared with the experimental data. The calculated results show that the optimized geometries can well reproduce the crystal structural parameters. The theoretical IR spectra and 13C and 1H NMR chemical shift values also show good agreement with experimental data. In addition, frontier molecular orbitals (FMO) and molecular electrostatic potential (MEP) analysis of the four isomers were investigated using theoretical calculations.