MOLECULAR STRUCTURE, MULLIKEN AND HOMO-LUMO ANALYSIS OF 1,2,4-TRIAZOLO[3,4-B]-1,3,4-THIADIAZINE BENZENESULFONAMIDE DERIVATIVES BASED ON DFT CALCULATIONS

Quantum chemical calculations on the geometric parameters, molecular electrostatic potential, natural bond orbital, mulliken atomic charges and nonlinear optical property of 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazine benzenesulfonamide derivatives 1-4 were performed using the density functional theory (DFT/B3LYP) methods with 6-31G (d,p) basis set. In MEP analysis, the negative charge covers the sulfamide function and the positive region is over the hydrogen atoms. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the compound 4. The results of natural bond orbital show that the electron density (ED) is in the * and π* anti-bonding orbitals, the second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. The calculated first hyperpolarizability of compound 1 is around one and half times that the value of the standard NLO material urea. Keywords: sulfamide; density functional theory; computational chemistry; quantum chemical calculations