苯的一取代物所起的亲电取代反应,根据大量实验事实归纳出下面的定位规律: 1.在苯环上新导入的取代基的位置主要由原有取代基来决定。2.可以把取代基分为两类:第一类取代基使新导入的基团进入邻位和对位,并且使反应易于进行(卤素除外);第二类定位基使新导入的取代基进入间位,并且使取代反应难于进行。要判断一个取代基属于哪一类,可利用一 The electrophilic substitution reaction of a substituted product of benzene can be summarized according to a large number of experimental facts: 1. The position of the newly introduced substituent on the benzene ring is mainly determined by the original substituent. 2. Substituents can be divided into two groups: The first group of substituents introduces newly introduced groups into the ortho and para positions, and allows the reaction to proceed easily (except for halogens); the second group of substituents allows for newly introduced substituents. Enter the meta-position and make the substitution reaction difficult. To determine which class a substituent belongs to, use one