甲基,乙基等是给电子取代基,氯甲基等是受电子取代基。这在有机化学上已得到公认。迄今人们一直认为所谓给电子取代基的电子效应是使反应活性部位的电子云密度增加,而受电子基团的作用是使反应活性部位的电子云密度降低。甲基取代导致烯烃亲电加成反应活性增加的原因,也用甲基的推电子作用造成 Methyl, ethyl and the like are electron-donating substituents, and chloromethyl and the like are electron-donating substituents. This has been recognized in organic chemistry. It has heretofore been considered that the so-called electron effect on electron-donating substituents is to increase the electron cloud density of the reactive sites, while the electron-accepting groups act to lower the electron cloud density of the reactive sites. The reason that the methyl substitution leads to an increase in the electrophilic addition reaction of olefins is also caused by the push electron effect of methyl groups