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分子几何构型的确定是研究分子的电子结构及其性质的第一步。一个分子的三维结构可以通过一组键长、键角和二面角来完全确定。其中,键长和键角一般与它们相应的标准值都很相近,即根据分子的拓扑结构给出的标准键长和键角与实际的键长和键角不会有太大的差别。因此,对于复杂的大分子,有时就不必考虑其微小的变化。分子的构象决定于二面角。所以二面角的变化最为敏感,确定分子的构象实际上就是确定二面角。如果一个分子中的全部二面角均已确定,那么分子的构象就已完全确定。在前文中,为了研究农药的定量构效关系,我们曾用从头算分子轨道方法对乙酰胆碱分子的几何构型进行了全优化,并同时用MOSMO方
The determination of molecular geometry is the first step toward studying the electronic structure of molecules and their properties. The three-dimensional structure of a molecule can be completely determined by a set of bond lengths, bond angles and dihedral angles. Among them, the bond length and bond angle are generally similar to their corresponding standard values, that is, the standard bond length and bond angle given by the molecular topology do not differ much from the actual bond length and bond angle. Therefore, for complex macromolecules, sometimes do not have to consider its minor changes. The molecular conformation is determined by the dihedral angle. Therefore, the change of the dihedral angle is the most sensitive. To determine the conformation of the molecule is actually to determine the dihedral angle. If all the dihedral angles in a molecule have been determined, the conformation of the molecule is completely determined. In the previous section, in order to study the quantitative structure-activity relationship of pesticides, we have fully optimized the geometrical configuration of the acetylcholine molecule using the ab initio molecular orbital method,