MOLECULAR STRUCTURE OF (E)-2-BROMO-1-[2-(2-NITROSTYRYL)-1-PHENYLSULFONYL-1H-INDOL-3-] ETHANONE AND ENERGY, FREQUENCY AND GEOMETRY COMPARSION WITH THE PARENT INDOLE STRUCTURE USIND DFT METHOD

Indole derivatives have been mostly reported to demonstrate significant activities such as analgesics, anti-inflammatory agents, antifungals, antiarrhythmic agents, and inhibitors of nitric oxide synthase. In this paper, indole derived compounds are believed to have antibiotic, anti-inflammatory, analgesic, antibacterial, anti-tumor, anti-fungal, anti-cancer and anti-AIDS virus activities [1]. Density functional theory (DFT) - a computational quantum mechanical modeling method-have become an impressive tool in the prediction of molecular calculations because approximate functional were shown to provide a useful balance between accuracy and computational cost [2]. In this paper, harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis and detonation properties of (E)-2-Bromo-1-[2-(2-nitrostyryl)-1-phenylsulfonyl-1H-indol-3-yl] ethanone is calculated. The solid phase FT-IR and FT-Raman spectra of C24H17BrN2O5S, were recorded in the region 4000–450 cm_1 and 4000–50 cm_1 respectively. Harmonic frequencies of this compound were determined and analyzed by DFT utilizing 6-31G(d,p), 6-31+G(d,p) basis sets. The assignments of the vibrational spectra have been carried out with the help of Normal Coordinate Analysis (NCA) following the Scaled Quantum Mechanical Force Field Methodology (SQMFF). The calculated infrared and Raman spectra of the title compounds were also stimulated utilizing the scaled force fields and the computed dipole derivatives for IR intensities and polarizability derivatives for Raman intensities. The change in electron density (ED) in the r* and p* antibonding orbital’s and stabilization energies E(2) have been calculated by Natural Bond Orbital (NBO) analysis to give clear evidence of stabilization originating in the hyperconjugation of hydrogen-bonded interaction. Heat of formation (HOF) and calculated density were estimated to evaluate detonation properties using Kamlet–Jacobs equations. The linear polarizability (a) and the first order hyperpolarizability (b) values of the investigated molecule have been computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. The observed and calculated wave numbers are found to be in good agreement. On the basis of vibrational analyses, the thermodynamic properties of title compound at different temperatures have been calculated [3]. Then the same calculations are done for the indole structure and are compared with the (E)-2-Bromo-1-[2-(2-nitrostyryl)-1-phenylsulfonyl-1H-indol-3-yl]ethanone calculations.