Kim Sunghwan, Wheeler Steven E, Deyonker Nathan J, Schaefer Henry F
Center for Computational Chemistry, University of Georgia, Athens, Georgia 30602, USA.
J Chem Phys. 2005 Jun 15;122(23):234313. doi: 10.1063/1.1926271.
The conformational behavior of oxalyl chloride has been investigated using ab initio Hartree-Fock (HF) and second-order Moller-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-zeta (cc-pVQZ) and quintuple-zeta (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[Double Bond]C-C[Double Bond]O dihedral angles of 81.9 degrees , 79.4 degrees , and 83.4 degrees , 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[Double Bond]C-C[Double Bond]O torsional mode is exceedingly flat. The existence of the gauche conformation is mainly due to the minimization of steric repulsion.
利用从头算哈特里-福克（HF）和二阶莫勒-普莱塞特（MP2）微扰理论以及附加微扰包含连接三重激发的耦合簇单双激发方法[CCSD(T)]，研究了草酰氯的构象行为。本研究使用了相关一致极化价四重zeta（cc-pVQZ）和五重zeta（cc-pV5Z）基组。在cc-pVQZ和cc-pV5Z HF水平下，不存在对应于稳定gauche构象异构体的驻点。另一方面，在cc-pVQZ和cc-pV5Z MP2水平以及使用cc-pVQZ CCSD(T)方法时，分别在O[双键]C-C[双键]O二面角为81.9度、79.4度和83.4度处发现了草酰氯的gauche构象异构体。在cc-pV5Z MP2水平下，预测从反式到gauche的能垒为0.74千卡摩尔⁻¹，从gauche到反式的能垒为0.09千卡摩尔⁻¹。因此，沿着O[双键]C-C[双键]O扭转模式的势能面非常平坦。gauche构象的存在主要是由于空间排斥的最小化。
