Vibrational spectral investigation and Natural Bond Orbital analysis of anti-rheumatoid drug Ethyl 4-nitrophenylacetate - DFT approach

Vibrational analysis of ethyl 4-nitrophenylacetate (ENPA) molecule was carried out using FT-IR and FT-Raman spectroscopic techniques. The equilibrium geometry, harmonic vibrational wave numbers, various bonding features have been computed using density functional theory. The calculated molecular geometry parameters have been compared with XRD data. The detailed interpretation of the vibrational spectra has been carried out by computing Potential Energy Distribution (PED). Stability of the molecule arising from hyperconjugative interactions and charge delocalization has been analyzed using Natural Bond Orbital (NBO) analysis. The results show that the charge in the electron density (ED) in the sigma* and pi* antibonding orbitals and second order delocalization energies (E-2) confirm the occurrence of ICT (intramolecular charge transfer) within the molecule. The simulated spectra satisfactorily coincide with the experimental spectra. (C) 2012 Elsevier B.V. All rights reserved.