在苯环的取代定位规律中,卤素是较特殊的定位基。它虽然是邻对位定位基,却使苯环钝化。例如:氯苯硝化反应的速度要比苯硝化反应的速度慢三十三倍。 对这种现象的解释,一般认为:卤素本身电负性大、使苯环上的电子密度普遍下降,导致亲电基团不易进攻,使苯环钝化。这种效应称之为诱导效应。当亲电基团终于结合在苯环上时,它可以形成若干种过渡态 In the benzene ring substitution rules, halogen is a more specific positioning base. Although it is adjacent to the positioning base, it makes the passivation of benzene. For example: chlorobenzene nitration reaction rate of benzene nitrification reaction slower than thirty-three times. The explanation of this phenomenon is generally believed that the halogen itself has a large electronegativity, which generally decreases the electron density on the benzene ring, resulting in that the electrophilic group is not easy to attack and the benzene ring is passivated. This effect is called the induction effect. When the electrophilic group finally binds to the benzene ring, it can form several transition states