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

► TTZ1 crystallizes in the monoclinic space group P2(1)/c. ► Theoretical structures, IR and NMR spectra of TTZ1-4 agree well with experiments. ► The electron transitions are corresponding to the n → π* and π → π* electron transitions. ► The negative and positive potential sites are around O and H atoms, respectively.