有两种不同的方法可用来解释化学位移随结构的变化。一种是用量子力学方法计算屏蔽常数和电子云密度,已在上一讲作了介绍;另一种是用统计方法分析实验数据。前者是处理一个分子中电子的贡献,用从头计算或半经验方法进行计算,而后者是大量分子的统计,得到不同分子间的联系。因而这两种方法是相 There are two different approaches that can be used to explain chemical shifts with structural changes. One is to use quantum mechanics to calculate the shielding constant and electron cloud density, has been introduced in the previous talk; the other is to use statistical methods to analyze experimental data. The former deals with the contribution of electrons in a molecule, calculated by ab initio or semi-empirical methods, while the latter is the statistics of a large number of molecules, obtaining the connection between different molecules. So these two methods are phases