Molecular structure, normal coordinate analysis, harmonic vibrational frequencies, NBO, HOMO–LUMO analysis and detonation properties of (S)-2-(2-oxopyrrolidin-1-yl) butanamide by density functional methods

Abstract

Density functional theory (DFT) computations have become an efficient tool in the prediction of molecular structure, harmonic force fields, vibrational wave numbers as well as the IR and Raman intensities of pharmaceutically important molecule. In this work, we report harmonic vibrational frequencies, molecular structure, NBO and HOMO, LUMO analysis and detonation properties of (S)-2-(2-oxopyrrolidin-1-yl) butanamide. The solid phase FT-IR and FT-Raman spectra of (S)-2-(2-oxopyrrolidin-1-yl) butanamide were recorded in the region 4000–450cm−1 and 4000–50cm−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 σ* and π* 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 (α) and the first order hyperpolarizability (β) 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.