亲电加成是烯烃的特征反应．在烯烃的亲电加成反应中，如果反应物烯烃是对称的分子，加成无择问问题；如果不对称试剂E—NU（E≠Nu）与不对称烯烃进行加成时，则可以生成两种加成产物．如：这两种可能性一般是不均等的，加成结果往往是其中一种产物占优势，或甚至只能得到一种 Electrophilic addition is the characteristic reaction of olefins. In the electrophilic addition of olefins, if the reactant olefin is a symmetric molecule, there is no optional addition problem; if the asymmetric reagent E-NU (E ≠ Nu) is added with the asymmetric olefin, it can be generated Two addition products. Such as: the two possibilities are generally unequal, the result of the addition is often one of the products dominate, or even get only one