定义Definition
区域选择性是指反应在分子中可能的几个位置（或方向）上优先在某一个位置发生的性质，生成的是构造异构体（区域异构体）之间的偏向。
Regioselectivity is the preference of a reaction for one of several possible positions or orientations in a molecule, favouring one constitutional isomer (regioisomer) over others.
典型规律Typical rules
马氏规则（HX 加成到不对称烯烃，H 加到含氢多的碳上）；反马氏（硼氢化、过氧化物存在下 HBr 自由基加成）；扎伊采夫与霍夫曼消除规则；芳环取代的邻、对位与间位定位；烯醇化的动力学与热力学控制；环氧化物酸性/碱性开环位置。
Markovnikov’s rule (H to the carbon with more H); anti-Markovnikov (hydroboration, radical HBr with peroxides); Zaitsev and Hofmann elimination rules; ortho/para versus meta direction in aromatic substitution; kinetic versus thermodynamic enolates; acid- versus base-catalysed epoxide opening.
根源Origins
中间体稳定性（更稳定的碳正离子、自由基、碳负离子）、位阻、电子效应（共振、诱导）和前线轨道系数（狄尔斯–阿尔德“邻/对位”规律）。
Intermediate stability (more stable cations, radicals, anions), sterics, electronic effects (resonance, induction) and frontier-orbital coefficients (the Diels–Alder ‘ortho/para’ rule).
术语Terminology
完全区域选择称“区域专一”（regiospecific，IUPAC 不推荐此用法）。
Complete preference is sometimes called ‘regiospecific’ (a usage IUPAC discourages).
年表Timeline
- 1870
马尔科夫尼科夫提出加成规则
Markovnikov formulates his addition rule
- 1933
卡拉施发现过氧化物效应
Kharasch discovers the peroxide effect