The ortho effect arises in certain electrophilic aromatic substitutions when a meta director is meta to an ortho/para director. Among the three expected isomer products, only the two isomers ortho to the meta director are produced normally. To find an explanation for the ortho effect, nitrations of two properly substituted benzenes were explored. Evidence supported an explanation based on resonance involving the meta director.

中文翻译：

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亲电子取代中邻位效应的基本原理

当间位导向剂与间位/对位导向键间位时，在某些亲电子芳族取代中会产生邻位效应。在这三种预期的异构体产物中，通常仅生成与元导子邻位的两种异构体。为了找到邻位效应的解释，研究了两个适当取代的苯的硝化作用。证据支持基于涉及元主管的共鸣的解释。