Conformations of Allyl Amine: Theory vs Experiment
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- 作者：Boris Galabov ; Sunghwan Kim ; Yaoming Xie ; Henry F. Schaefer III ; Matthew L. Leininger ; James R. Durig
- 刊名：Journal of Physical Chemistry A
- 出版年：2008
- 出版时间：March 13, 2008
- 年：2008
- 卷：112
- 期：10
- 页码：2120 - 2124
- 全文大小：54K
- 年卷期：v.112,no.10(March 13, 2008)
- ISSN：1520-5215
文摘
The relative stabilities of the five conformers of allyl amine, a medium-size aliphatic molecule, were estimatedby applying ab initio quantum mechanical methods at several levels of theory. The second-order M
ller-Plesset perturbation method (MP2), quadratic configuration interaction including single and double excitations(QCISD), coupled-cluster with single and double excitations (CCSD) and CCSD plus perturbative tripleexcitations [CCSD(T)] were applied. The Dunning correlation consistent basis sets (through aug-cc-pVQZand cc-pV5Z) were employed. The MP2 energies relative to the energy of the cis-trans conformer reportedhere appear to approach the basis set limit. The predicted allyl amine conformer energies approaching theHartree-Fock basis set limit are 158 cm-1 (cis-gauche), -5 cm-1 (gauche-trans), and -146 cm-1 (gauche-gauche). The same three relative energies near the MP2 basis set limit are 135, 103, and 50 cm-1, respectively.The analogous energies deduced from experiment are 173 ± 12, 92 ± 8, and 122 ± 5 cm-1. The theoreticalresults obtained in the present study suggest that satisfactory predictions of the conformer energetics of allylamine may be achieved only by theoretical methods that incorporate consideration of correlation effects inconjunction with large basis sets. Evaluation of the zero-point vibrational energy corrections is critical, dueto the very small classical energy differences between the five conformers of allyl amine. Agreement betweentheory and experiment for the gauche-gauche conformational energy remains problematical.
ller-Plesset perturbation method (MP2), quadratic configuration interaction including single and double excitations(QCISD), coupled-cluster with single and double excitations (CCSD) and CCSD plus perturbative tripleexcitations [CCSD(T)] were applied. The Dunning correlation consistent basis sets (through aug-cc-pVQZand cc-pV5Z) were employed. The MP2 energies relative to the energy of the cis-trans conformer reportedhere appear to approach the basis set limit. The predicted allyl amine conformer energies approaching theHartree-Fock basis set limit are 158 cm-1 (cis-gauche), -5 cm-1 (gauche-trans), and -146 cm-1 (gauche-gauche). The same three relative energies near the MP2 basis set limit are 135, 103, and 50 cm-1, respectively.The analogous energies deduced from experiment are 173 ± 12, 92 ± 8, and 122 ± 5 cm-1. The theoreticalresults obtained in the present study suggest that satisfactory predictions of the conformer energetics of allylamine may be achieved only by theoretical methods that incorporate consideration of correlation effects inconjunction with large basis sets. Evaluation of the zero-point vibrational energy corrections is critical, dueto the very small classical energy differences between the five conformers of allyl amine. Agreement betweentheory and experiment for the gauche-gauche conformational energy remains problematical.