苯环的亲电取代定位效应（英语：Orientation effect of electrophilic aromatic directing groups）是指苯环上已有的取代基对亲电取代反应的影响。1895年霍里曼（Holleman）等从大量实验事实中归纳出这一规律。主要有两种影响：一、活化苯环，有利于亲电取代反应的发生；二、钝化苯环，不利于亲电取代反应的发生。

In organic chemistry, an electron donating group (EDG) or electron releasing group (ERG) is an atom or functional group that donates some of its electron density into a conjugated π system via resonance or inductive electron withdrawal, thus making the π system more nucleophilic. When attached to a benzene molecule, an electron donating group makes it more likely to participate in electrophilic substitution reactions. Benzene itself will normally undergo substitutions by electrophiles, but additional substituents can alter the reaction rate or products by electronically or sterically affecting the interaction of the two reactants. EDGs are often known as activating groups.