定义Definition
重排反应是分子中原子或基团从一个位置迁移到另一个位置，使碳骨架或官能团位置改变，生成结构异构体的反应。
A rearrangement reaction moves an atom or group from one position to another within a molecule, changing the carbon skeleton or functional-group position to give a structural isomer.
按机理分类Classification by mechanism
①缺电子中心的 1,2-迁移：碳正离子（瓦格纳–梅尔外因、频哪醇）、氮宾/缺电子氮（霍夫曼、库尔提斯、贝克曼）、缺电子氧（贝耶尔–维利格）；②富电子中心迁移：法沃斯基、维蒂希重排；③周环 σ 迁移：克莱森、科普重排；④自由基重排。
(1) 1,2-shifts to electron-deficient centres: carbocations (Wagner–Meerwein, pinacol), electron-poor nitrogen (Hofmann, Curtius, Beckmann), oxygen (Baeyer–Villiger); (2) migrations to electron-rich centres: Favorskii, Wittig rearrangements; (3) pericyclic sigmatropic shifts: Claisen, Cope; (4) radical rearrangements.
迁移规律Migration rules
1,2-迁移中迁移基团通常保持构型；迁移能力与基团稳定正电荷的能力相关（叔烷基、芳基较强）；驱动力来自生成更稳定的中间体或产物（更稳定的碳正离子、强 C=O 键、环张力释放）。
Migrating groups usually keep their configuration; aptitude follows their ability to stabilise positive charge (tertiary alkyl, aryl); the driving force is a more stable intermediate or product (better cation, strong C=O, ring-strain relief).
意义Significance
重排既可能是不希望的副反应（如傅–克烷基化、SN1），也是构建复杂骨架的有力工具（扩环、缩环、季碳中心、手性传递）。生物合成中萜类、甾体的环化伴随大量重排。
Rearrangements can be unwanted side reactions (Friedel–Crafts alkylation, SN1) or powerful tools for ring expansion and contraction, quaternary centres and chirality transfer; terpene and steroid biosynthesis is full of them.
反应Reactions
酸、碱、加热或光照，视具体重排而定
Acid, base, heat or light depending on the rearrangement
生成活性中心（碳正离子、缺电子氮等）或进入周环过渡态。
An active centre forms (cation, electron-poor N) or a pericyclic TS is reached.
基团迁移。
The group migrates.
新中间体转化为稳定产物。
The new intermediate becomes the stable product.
尼龙-6 单体。
The nylon-6 monomer.
反应机理图Mechanism
红色弯箭头表示一对电子的移动方向：从电子来源（孤对电子或化学键）指向电子去向。Red curly arrows show where an electron pair moves: from its source (lone pair or bond) to its destination.
甲基带着电子对迁移到相邻的正碳上
A methyl moves with its electron pair to the adjacent cationic carbon
仲碳正离子变成更稳定的叔碳正离子
The secondary cation becomes a more stable tertiary one
年表Timeline
- 1828
维勒由氰酸铵制得尿素（异构化）
Wöhler converts ammonium cyanate into urea (an isomerisation)
- 1860
频哪醇重排
Pinacol rearrangement
- 1886
贝克曼重排
Beckmann rearrangement
- 1912
克莱森重排
Claisen rearrangement