Spectroscopic, Structural, Aromaticity and Electronic Properties of Isatoic Anhydride - Experimental and Theoretical Investigations

The paper compares the experimental FT-IR, 1H- and 13C-NMR spectra of isatoic anhydride (ISA) with the Hartree-Fock (HF) and Density Functional Theory (DFT) calculations using three different basis sets (6-31+G(d,p), 6-311+G(d,p), cc-pVTZ). The best compatibility between the experimental and theoretical FT-IR spectrum was observed with the use of B3LYP/6-31+G(d,p) method for ISA. Furthermore, the theoretical1H- and 13C-NMR spectra interpreted by GIAO method depict that the DFT formalism, particularly the B3LYP/6-311+G(d,p) theory of level, gives an accurate description of the ISA experimental chemical shifts. The calculated structural data were also compared with experimental findings. The statistical regression analyses show that the B3LYP/6-31+G(d,p) method results in a correct description of the ISA crystallographic data. Moreover, the frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP) map, and NBO atomic charges of the ISA have been discussed at B3LYP/6-31+G(d,p) theory of level. The FMO analysis were used to determine the charge transfer within ISA and some chemical descriptors such as ionization potential, electron affinity, chemical hardness, softness, chemical potential and electro negativity. The Nucleus-Independent Chemical Shifts (NICS) were also computed for ISA derivatives, 2-10. In the X: O and Y: S derivative, 4, sulphur substitution increases slightly the aromaticity of ISA skeleton