Wiberg Kenneth B
Department of Chemistry, Yale University, 225 Prospect Street, P.O. Box 208107, New Haven, Connecticut 06520-8107, USA.
J Org Chem. 2003 Nov 28;68(24):9322-9. doi: 10.1021/jo030227n.
The conformers of cycloheptane through cyclodecane have been examined at the B3LYP/6-311+G* and MP2/6-311+G* theoretical levels, with some additional calculations at the CCD/6-311+G* and CCSD(T)/6-311++G** levels. With cyclooctane, B3LYP predicts that the boat-chair and crown conformers have similar energies, whereas MP2 and CCSD(T) predict that the crown conformer is 2 kcal/mol higher in energy. The latter is in agreement with the electron diffraction data. With cyclononane, B3LYP predicts that two of the higher-energy conformers found in molecular mechanics calculations should convert to one of the lower-energy conformers. However, MP2/6-311+G* optimizations find them to be true minima on the potential energy surface. B3LYP systematically predicts larger C-C-C bond angles for these compounds than either MP2 or CCD. The results of molecular mechanics MM4 calculations are generally in good agreement with those obtained using MP2.
已在B3LYP/6 - 311 + G和MP2/6 - 311 + G理论水平下研究了环庚烷至环癸烷的构象异构体，并在CCSD/6 - 311 + G和CCSD(T)/6 - 311++G**水平下进行了一些额外计算。对于环辛烷，B3LYP预测船椅式和皇冠式构象异构体具有相似的能量，而MP2和CCSD(T)预测皇冠式构象异构体的能量高2千卡/摩尔。后者与电子衍射数据一致。对于环壬烷，B3LYP预测在分子力学计算中发现的两个高能构象异构体应转化为一个低能构象异构体。然而，MP2/6 - 311 + G优化发现它们是势能面上的真实极小值。B3LYP系统地预测这些化合物的C - C - C键角比MP2或CCSD的更大。分子力学MM4计算结果通常与使用MP2获得的结果非常一致。
