COMPUTATIONAL STUDY OF GEOMETRY, IR SPECTRUM AND MOLECULAR PROPERTIES OF ACETIC ACID
Mohammad Firoz Khan, Ridwan Bin Rashid, Md. Al-Faruk and Mohammad A. Rashid
ABSTRACT
In this paper an effort was made to conduct and repot a computational study of geometry, IR spectrum, solvation free energy, dipole moment and different molecular properties like Molecular Electrostatic Potential (MESP), Mulliken Charge Distribution, Global and Local Reactivity Descriptors (chemical hardness, softness, chemical potential, electronegativity, electrophilicity index) etc. of acetic acid. Hartee–Fock (HF), Becke, 3-parameter, Lee-Yang-Parr (B3LYP) and second order Møller–Plesset (MP2) perturbation theory were employed for all models, both in gas phase and in solution, with basis sets up to 6-311+G(d,p) for HF and B3LYP and 6-31G(d) for MP2. A new solvation model, solvation model on density (SMD) was also used for solvation free energy and dipole moment calculations. The calculated
geometries (bond length, bond angle and dihedral angle) were in a good agreement with the experimental data for all level of theory and basis sets. In case of IR frequencies the scaled calculated frequencies agreed reasonably well with the experimental results. The solvation free energy and dipole moment of acetic acid was increased when going from non-polar to polar solvents for both polarizable continuum model (PCM) and SMD model. However, with SMD the solvation free energies were higher than those of PCM in all the solvent system (water (H2O), dimethyl sulfoxide (DMSO) and chloroform (CHCl3). The computed geometrical parameters and scaled frequencies were found in close agreement with the experimental data. Moreover, the calculated solvation free energy, dipole moment and molecular properties may lead to the understanding of miscibility, stability and activity of acetic acid.
Keywords: Acetic acid, Polarizable continuum model, Vibrational frequency, Solvation free energy, Molecular electrostatic potential.
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