Sunghwan Kim - Conformations of allyl amine: Theory vs experiment

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  Publication Details (including relevant citation   information):

  B. Galabov, S.   Kim, Y. Xie, H.F. Schaefer, M.L. Leininger, and J.R.   Durig;

  Journal of Physical Chemistry A,  2008, 112, 2120.



  The relative stabilities of the five conformers of allyl amine, a   medium-size aliphatic molecule, were estimated by applying ab   initio quantum mechanical methods at several levels of theory.   The second-order Møller-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 triple excitations   [CCSD(T)] were applied. The Dunning correlation consistent basis   sets (through aug-cc-pVQZ and cc-pV5Z) were employed. The MP2   energies relative to the energy of the cis - trans conformer   reported here appear to approach the basis set limit. The   predicted allyl amine conformer energies approaching the Hartree   - 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   theoretical results obtained in the present study suggest that   satisfactory predictions of the conformer energetics of allyl   amine may be achieved only by theoretical methods that   incorporate consideration of correlation effects in conjunction   with large basis sets. Evaluation of the zero-point vibrational   energy corrections is critical, due to the very small classical   energy differences between the five conformers of allyl amine.   Agreement between theory and experiment for the gauche - gauche   conformational energy remains problematical.


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