Physical analysis of aspirin in different phases and states using density functional theory

Abstract

This study analyzed the aspirin molecule (C9H8O4) using Density Functional Theory (DFT) on Gaussian 09W software. First, the structure of aspirin was optimized using the DFT method with the B3LYP functional and the 6-311+G (d,p) basis set. A global reactivity study was employed to understand the reactivity of aspirin in gas and solvent water for both anion and neutral states. To understand the involvement of orbitals in chemical stability and electron conductivity, we calculated the HOMO-LUMO. The thermodynamic function of a molecule was understood using thermochemistry. Molecular Electrostatic Potential (MEP) was employed to understand the physiochemical properties of aspirin. We observed the Mulliken atomic charge to calculate the atomic charge of aspirin. Finally, the title molecule's UV-Vis, FTIR, and Raman spectra are analyzed and compared with the experimental data.

Keywords: DOS; HOMO AND LUMO; MEP; Mulliken atomic charge; Spectroscopy.

Fig. 1

Optimized structure of aspirin with labelled atoms.

Fig. 2

HOMO, LUMO and energy gap of aspirin in neutral state in (a) gas phase (b) water solvent.

Fig. 3

HOMO, LUMO, and energy gap of aspirin in anion state in (a) gas phase b) solvent water.

Fig. 4

DOS spectra of aspirin molecule in a a neutral state in a) gas phase and b) water solvent.

Fig. 5

DOS spectra of aspirin molecule in anion state a) gas phase a) water solvent.

Fig. 6

MEP map of aspirin in a) neutral state and b) anion state.

Fig. 7

Mulliken charge distribution chart of the aspirin molecule in neutral and anion state.

Fig. 8

FT-IR spectra of aspirin in the gas phase for fingerprint region.

Fig. 9

Raman spectra of aspirin for a) neutral and b) anion state in gas phase.

Fig. 10

Raman spectra of aspirin for a) neutral and b) anion state in solvent water.

Fig. 11

UV–Vis spectra and Tauc plot of aspirin for a) neutral and b) anion state in water solvent.