5th WCSET-2016 at Vietnam
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