Synthesis, Crystal Structure and Spectroscopic Properties of 1,2-Benzothiazine Derivatives: An Experimental and DFT Study

1,2-Benzothiazine derivatives methyl 3-methoxy-4-oxo-3,4-dihydro-2H-benzo[e] [1,2]thiazine-3-carboxylate 1,1-dioxide(1) and methyl 2-ethyl-3-hydroxy-4-oxo-3,4-dihydro-2Hbenzo[e][1,2]thiazine-3-carboxylate 1,1-dioxide(2) were synthesized, and characterized by spectroscopic techniques; 1H-NMR and infrared(IR) spectroscopy. Crystals of 1 and 2 were grown by slow evaporation of methanol and ethyl acetate, respectively and their crystal structures were investigated by single-crystal X-ray diffraction analysis. Geometric properties were calculated by the B3 LYP method of density functional theory(DFT) at the 6-31G+(d) basis set to compare with the experimental data. Simulated properties were found in strong agreement with the experimental ones. Intermolecular forces have also been modeled in order to investigate the strength of packing and strong hydrogen bonding was observed in both compounds 1 and 2. Electronic properties such as Ionization Potential(IP), Electron Affinities(EA) and coefficients of the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO) of com- pounds 1 and 2 were simulated for the first time.