TY - JOUR
T1 - Staggered and eclipsed conformations of C2F6
T2 - A systematic ab initio study
AU - Parra, Rubén D.
AU - Zeng, X. C.
N1 - Funding Information:
R.D.P. is grateful to Joy Woller for critical reading of the manuscript, and to Mark Gibson and E. Rajasekaran for useful discussion. This work was supported by the National Science Foundation and the Office of Naval Research (X.C.Z) .
PY - 1997/6
Y1 - 1997/6
N2 - Molecular geometries, energies, and vibrational frequencies for eclipsed and staggered conformers of perfluoroethane were determined by ab initio calculations. Basis set effects were investigated systematically with progressively larger basis sets, up to triple zeta, d and f polarization functions plus diffuse functions on all atoms. Electron correlation was included by means of Møller-Plesset perturbation calculations to the third order. Vibrational frequencies, calculated at both Hartree-Fock (HF) and second order Møller-Plesset perturbation (MP2) methods, were used to make zero-point energy and thermal corrections to electronic energies. Some semi-empirical methods and molecular mechanics force fields were also employed for comparison. The rotational barrier (3.81 kcal mol-1) predicted from the HF/6-311+G(3df) method is close to the measured electron diffraction value of 4.40 kcal mol-1 (-0.90,+1.10). The MP2/6-311G(d) level gives a lower barrier of 3.33 kcal mol-1, and the best MP3 calculation, MP3/6-311+G(3df)//MP2/6-311G(d), a value of 3.55 kcal mol-1.
AB - Molecular geometries, energies, and vibrational frequencies for eclipsed and staggered conformers of perfluoroethane were determined by ab initio calculations. Basis set effects were investigated systematically with progressively larger basis sets, up to triple zeta, d and f polarization functions plus diffuse functions on all atoms. Electron correlation was included by means of Møller-Plesset perturbation calculations to the third order. Vibrational frequencies, calculated at both Hartree-Fock (HF) and second order Møller-Plesset perturbation (MP2) methods, were used to make zero-point energy and thermal corrections to electronic energies. Some semi-empirical methods and molecular mechanics force fields were also employed for comparison. The rotational barrier (3.81 kcal mol-1) predicted from the HF/6-311+G(3df) method is close to the measured electron diffraction value of 4.40 kcal mol-1 (-0.90,+1.10). The MP2/6-311G(d) level gives a lower barrier of 3.33 kcal mol-1, and the best MP3 calculation, MP3/6-311+G(3df)//MP2/6-311G(d), a value of 3.55 kcal mol-1.
KW - Ab initio
KW - Perfluoroethane
KW - Rotational barrier
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U2 - 10.1016/S0022-1139(96)03573-7
DO - 10.1016/S0022-1139(96)03573-7
M3 - Article
AN - SCOPUS:0031161105
VL - 83
SP - 51
EP - 60
JO - Journal of Fluorine Chemistry
JF - Journal of Fluorine Chemistry
SN - 0022-1139
IS - 1
ER -