Ab initio calculations and internal rotor: Contribution for thermodynamic properties S°298 and Cp(T)'s (300 < T/K < 1500): Group additivity for fluoroethanes

Document Type

Article

Publication Date

9-10-1998

Abstract

Ab initio calculations are performed on nine fluorinated ethane compounds and thermodynamic properties (S°298 and Cp(T)'s 300 < T/K < 1500) are calculated. Geometries of stable rottional conformers and transition states for internal rotation are optimized at the RHF/6-31G* (6-31G(d))and MP2/6-31G* levels of theory. Harmonic vibrational frequencies are computed at the RHF/6-31G* level of theory. Potential barriers for internal rotations are calculated at the MP2/6-31G*//MP2/6-31G* level. Parameters of the Fourier expansion of the hindrance potential are tabulated. Standard entropies (S°298) and heat capacities (Cp(T)'s, 3 < T/K < 1500) are calculated using the rigid-rotor-harmonic-oscillator approximation with direct integration over energy levels of the intramolecular rotation potential energy curve. Heats of formation are adopted from literature evaluation and BAC-MP4 ab initio calculations. Thermodynamic properties for fluorinated carbon groups C/C/F/H2, C/C/F2/H, and C/C/F3 are determined by existing thermodynamic group parameter of C/C/H3 and data on CH2FCH3, CHF2CH3, and CF3CH3, respectively: no fluorine or other halogen is on the methyl carbon adjacent to the carbon bonded to the fluorine(s). Six interaction terms in addition to the above groups are developed to account for repulsion and steric effects. Interaction terms are required to accurately estimate ΔHf°298, S°298, and Cp(T)'s (300 < T/K < 1500) for fluoroethanes where fluorine(s) are on carbons adjacent to a carbon bonded to fluorine(s).

Identifier

4244185549 (Scopus)

Publication Title

Journal of Physical Chemistry A

External Full Text Location

https://doi.org/10.1021/jp980951n

ISSN

10895639

First Page

7286

Last Page

7293

Issue

37

Volume

102

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