Electrophilic addition is the characteristic reaction of alkenes, in which an electrophile adds to the electron-rich carbon–carbon double bond (C=C). The π electrons of the double bond attack the electrophile, forming a carbenium ion, which is then captured by a nucleophile to complete the addition. It matters because it is the main route by which the unreactive double bond is functionalised, for example in hydration and halogenation. It contrasts with the nucleophilic addition typical of the electron-poor carbonyl group.

亲电加成是烯烃的特征反应,其中亲电试剂加到富电子的碳碳双键(C=C)上。双键的 π 电子进攻亲电试剂,生成碳正离子,后者再被亲核试剂捕获以完成加成。它之所以重要,是因为它是使不活泼的双键官能化的主要途径,例如在水合和卤化中。它与缺电子羰基典型的亲核加成形成对照。