不同构象表示法使用Cram规则的探讨

Application of Cram Rules in Different Conformational Expressions

Cram经验规则在判断与手性中心相连羰基的亲核加成立体选择性方面具有重要应用,目前教材常采用Newman投影式结合Cram规则进行主要产物的预测,而当Cram规则使用于其他构象表示式如锯架式、伞形式及Fischer投影式时,需要先进行构象转换,这对学生的空间想象能力及抽象思维提出较高要求,导致在判断时容易出错,是有机化学学习的一个难点。通过对Cram规则的深入分析,介绍Cram规则如何直接应用于除Newman表示式外的常用构象表示式,以避免费时费力又容易出错的构象式转化。

Cram empirical rules have important applications in judging nucleophilic addition stereoselectivity of carbonyl group having a proximal stereocenter. Newman projection combined with Cram rule is often used to predict main products in current textbooks. Other commonly used conformational expressions such as saw frame, umbrella frame and Fischer projection often require conformational transformation when Cram rules are used. However, this transformation has high requirements on spatial imagination and abstraction, and is prone to errors in learning. It is a difficulty in organic chemistry learning. In this paper, the use of Cram rules is directly discussed through in-depth analysis by using other commonly used conformational expressions, such as saw frame, umbrella frame and Fischer projection, so as to avoid the transformation between conformational expressions that are free of charge, laborious and prone to errors.