Sunghwan Kim - The extremely flat torsional potential energy surface of oxalyl chloride

Version 3

      Publication Details (including relevant citation   information):

      S. Kim, S.E.   Wheeler, N.J. Deyonker, H.F. Schaefer;

      Journal of Chemical Physics,   2005122, 234313.



      The conformational behavior of oxalyl chloride has been   investigated using ab initio Hartree-Fock (HF) and second-order   Møller-Plesset (MP2) perturbation theories, and the   coupled-cluster singles and doubles method appended with a   perturbative inclusion of connected triple excitations [CCSD(T)].   Correlation consistent polarized valence quadruple- ζ (cc-pVQZ)   and quintuple- ζ (cc-pV5Z) basis sets were used in this research.   At the cc-pVQZ and cc-pV5Z HF levels, there is no stationary   point corresponding to a stable gauche conformer. On the other   hand, at the cc-pVQZ and cc-pV5Z MP2 levels and with the cc-pVQZ   CCSD(T) method, the gauche conformer of oxalyl chloride was found   at O=C-C=O dihedral angles of 81.9°, 79.4°, and 83.4°,   respectively. At the cc-pV5Z MP2 level, the energy barrier from   trans to gauche was predicted to be 0.74 kcal mol-1 and that from   gauche to trans to be 0.09 kcal mol-1. Thus, the potential-energy   surface along the O=C-C=O torsional mode is exceedingly flat. The   existence of the gauche conformation is mainly due to the   minimization of steric repulsion.


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