Technical Session - 1

Title:            A revisit of thermodynamic properties of ethanol – a theoretical approach
Authors:       Tuan Q. Mach, Lam K. Huynh
Abstract:     In this study we investigate the effect of the ratio of the two conformers, gauche and anti, on the
thermodynamic properties of ethanol using accurate ab initio calculations and modern statistical calculations. Specifically, accurate electronic structure calculations at the composite CBS-QB3 method were carried out to determine stable structures and their molecular properties (e.g., vibrational frequencies, rotational constants, etc.). Within the statistical mechanics framework, the calculated molecular properties were used to calculate thermodynamic properties with the inclusion of the rigorous hindered internal rotation (HIR) treatment for the rotation of the CH3 group along the C-C bond. The thermodynamic properties of ethanol can be calculated by averaging those of the two conformers using Keq and then compared with literature data. Alternatively, the data were also calculated using the most stable conformer, anti, with the implicit inclusion of the gauche conformer through the HIR treatment of the OH group along the C-O bond. The results from two approaches are in good agreement with the literature data for heat of formation (?fH), entropy (S) and heat capacity (Cp) for a wide temperature range. Since the later approach is less expensive, it is recommended to use for larger alcohol systems where it is very time-consuming to explore all possible conformers.

Keywords:  Ethanol, Conformers, Thermodynamic Properties, Hindered Internal Rotation, CBS-QB3.
Pages:        039-043

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