邻基参与效应，有机化学概念之一，指的是相邻基团含有的σ键、π键电子或孤对电子与反应中心发生作用，使反应的某些性质发生改变的现象。邻基参与效应的典型现象为：反应速率加快（邻助效应），产物具有异常的立体化学特征（如亲核取代反应中的构型保持），反应涉及环状过渡态或中间体，反应中发生重排，等等。

一般指邻基参与效应，指的是杂原子孤对电子对S_N2反应的协助及桥环化合物和π体系对碳正离子的稳定作用。其实这个效应的范围很广，比如狄尔斯-阿尔德反应中连有不饱和基团的亲双烯体与双烯体之间的次级轨道作用，使得内型加成物成为动力学控制产物的现象，就是邻基参与效应的一个例子。邻基参与反应的历程主要有三类 ,即n—参与历程、π—参与历程和σ—参与历程 ;分为二步 :( 1)反应物的邻基从反面进攻α—碳原子 ,形成中间体 ,构型转化一次 ,为分子内的S_N2反应 ;( 2 )外部的亲核试剂Nu从邻基的反面进攻中间体 ,构型又转化一次 ,再发生一次分子内SN2反应 ,其结果是 :该类反应总的来说属于S_N1反应历程 ,产物的构型保持不变。

Neighbouring group participation (NGP) (also known as anchimeric assistance) in organic chemistry has been defined by IUPAC as the interaction of a reaction centre with a lone pair of electrons in an atom or the electrons present in a sigma bond or pi bond . When NGP is in operation it is normal for the reaction rate to be increased. It is also possible for the stereochemistry of the reaction to be abnormal (or unexpected) when compared with a normal reaction. While it is possible for neighbouring groups to influence many reactions in organic chemistry (e.g. the reaction of a diene such as 1,3-cyclohexadiene with maleic anhydride normally gives the endo isomer because of a secondary effect {overlap of the carbonyl group π orbitals with the transition state in the Diels-Alder reaction}) this page is limited to neighbouring group effects seen with carbocations and S_N2 reactions.