周环反应中的“4n光对”规则

The Rule of "4 nlight on" in Pericyclic Reaction

＂4n光对＂规则主要应用于环加成反应与电环化反应中,亦可应用于简单迁移反应,＂4n＂指的是参加反应的π电子数,＂光＂指的是反应条件为光照,＂对＂指的是在环加成反应中为对称性允许、在电环化反应中为对旋。利用＂4n光对＂规则可以简单判断有机化学教材中前述反应的立体选择性特点,并对预测复杂和未知的反应提供参考性依据,此方法简单易懂,便于记忆。

This article focused on the rule of ＂4nlight on＂ and its application to pericyclic reactions,electrocyclic reactions and migration reactions. ＂4n＂ refers to the number ofπelectrons in the reaction, ＂light＂ means the reaction condition and ＂on＂ refers to the symmetry-permission in pericyclic reaction and anticlockwise rotation in electrocyclic reaction.The rule can be used to conjecture the stereoselectivity of these reactions and provide crucial basis for prediction of complex and unknown reactions.Moreover,the rule is simple and easier to remember.