Enthalpy Differences of the n-Pentane Conformers.
The energy and enthalpy differences of alkane conformers in various temperature ranges have been the subject for both experimental and theoretical studies over the last few decades. It was shown previously for the conformers of butane [G. Tasi et al., J. Chem. Theory Comput. 2012, 8, 479-486] that quantum chemical results can compete with spectroscopic techniques and results obtained even from the most carefully performed experiments could be biased due to the improper statistical model utilized to evaluate the raw experimental data. In the current study, on one hand, the experimental values and their uncertainties for the enthalpy differences for pentane conformers are re-evaluated using the appropriate statistical model. On the other hand, a coupled-cluster-based focal-point analysis has been performed to calculate energy and enthalpy differences for the conformers of pentane. The model chemistry defined in this study includes contributions up to the perturbative quadruple excitations augmented with further small correction terms beyond the Born-Oppenheimer and nonrelativistic approximations. Benchmark quality energy and enthalpy differences for the pentane conformers are given at temperatures 0 and 298.15 K as well as for the various temperature ranges used in the gas-phase experimental measurements. Furthermore, a slight positive shift for the experimental enthalpy differences is also predicted due to an additional Raman active band belonging to the gauche-gauche conformer.
MTA-BME Lendület Quantum Chemistry Research Group, Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics , H-1521 Budapest, P.O. Box 91, Hungary.
József
J
Csontos
MTA-BME Lendület Quantum Chemistry Research Group, Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics , H-1521 Budapest, P.O. Box 91, Hungary.|Department of Chemistry, Aarhus University , Langelandsgade 140, 8000 Aarhus, Denmark.
Balázs
B
Nagy
Department of Applied and Environmental Chemistry, University of Szeged , Rerrich B. tér 1., H-6720 Szeged, Hungary.
László
L
Gyevi-Nagy
MTA-BME Lendület Quantum Chemistry Research Group, Department of Physical Chemistry and Materials Science, Budapest University of Technology and Economics , H-1521 Budapest, P.O. Box 91, Hungary.
Mihály
M
Kállay
Department of Applied and Environmental Chemistry, University of Szeged , Rerrich B. tér 1., H-6720 Szeged, Hungary.
Gyula
G
Tasi