Chemistry Department, Faculty of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia.
J Mol Graph Model. 2013 Sep;45:137-43. doi: 10.1016/j.jmgm.2013.08.004. Epub 2013 Aug 20.
Conformational analysis was performed for 18-thiacrown-6 (18t6) using the CONFLEX method and the MMFF94s force field. Computations were performed for some of the low energy conformations at the HF, B3LYP, CAM-B3LYP, M06, M06L, M062x, M06HF and MP2 levels. The computations were also performed using the DFT-D3 method along with the TPSS and PBE functionals. The study predicted a new C2 conformation as the ground state conformation of 18t6. This new C2 conformation is more stable than the experimentally known solid state conformation by 4.7 kcal/mol at the MP2/6-311G** level. This conformation has all of the SCCS dihedral angles adopt exodentate structure. However, the experimentally known conformation of the solid phase has two of the SCCS dihedral angles violating this exodentate rule. It was concluded that for 18t6 stability a linear dihedral SCCS angle requirement is more important than a gauche CSCC dihedral angle requirement.
采用 CONFLEX 方法和 MMFF94s 力场对 18-硫代冠-6（18t6）进行构象分析。在 HF、B3LYP、CAM-B3LYP、M06、M06L、M062x、M06HF 和 MP2 能级下对一些低能量构象进行了计算。还使用 DFT-D3 方法以及 TPSS 和 PBE 泛函进行了计算。研究预测了一种新的 C2 构象作为 18t6 的基态构象。这种新的 C2 构象在 MP2/6-311G** 水平上比实验已知的固态构象稳定 4.7 kcal/mol。这种构象具有所有的 SCCS 二面角采用外齿结构。然而，实验中已知的固相构象有两个 SCCS 二面角违反了这种外齿规则。得出的结论是，对于 18t6 的稳定性，线性二面 SCCS 角的要求比 gauche CSCC 二面角的要求更重要。
