定义Definition
亲核加成是亲核试剂进攻缺电子的不饱和键碳（最典型为羰基碳），π 键断开、电子移到电负性原子上，再经质子化完成加成的反应。
Nucleophilic addition is attack of a nucleophile on an electron-poor unsaturated carbon — typically a carbonyl carbon — breaking the π bond so the electrons move onto the electronegative atom, followed by protonation.
羰基加成Carbonyl additions
亲核试剂沿约 107° 的伯吉–邓尼茨角接近羰基碳，碳由 sp² 变为 sp³，生成烷氧负离子，再质子化成醇。常见亲核试剂：H⁻（NaBH₄、LiAlH₄）、R⁻（格氏、有机锂）、CN⁻（氰醇）、ROH（半缩醛、缩醛）、RNH₂（亚胺）、亚硫酸氢根、叶立德（维蒂希）。
Nucleophiles approach the carbonyl carbon along the ~107° Bürgi–Dunitz trajectory; carbon goes from sp² to sp³, giving an alkoxide that is protonated to the alcohol. Typical nucleophiles: H⁻ (NaBH₄, LiAlH₄), R⁻ (Grignard, organolithium), CN⁻ (cyanohydrins), ROH (hemiacetals, acetals), RNH₂ (imines), bisulfite and ylides (Wittig).
活性顺序Reactivity
甲醛 > 其他醛 > 酮：烷基给电子并增加位阻，降低羰基碳亲电性；芳基共轭也降低活性。三氯乙醛、六氟丙酮极易与水加成生成稳定水合物。
Formaldehyde > other aldehydes > ketones, because alkyl groups donate electrons and add steric bulk; aryl conjugation lowers reactivity. Chloral and hexafluoroacetone form stable hydrates.
立体化学Stereochemistry
平面羰基两面受进攻概率相同时得外消旋体；分子中已有手性中心时按克拉姆、费尔金–安模型给出非对映选择性。
Equal attack on both faces gives racemates; existing stereocentres give diastereoselectivity described by the Cram and Felkin–Anh models.
反应Reactions
视亲核试剂而定
Depends on the nucleophile
亲核试剂进攻羰基碳。
The nucleophile attacks the carbonyl carbon.
生成四面体烷氧负离子。
A tetrahedral alkoxide forms.
质子化得加成产物。
Protonation gives the adduct.
生成氰醇。
Cyanohydrin formation.
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.
亲核试剂进攻羰基碳，π 电子移到氧上
The nucleophile attacks the carbonyl carbon; the π electrons move to O
四面体烷氧负离子质子化
The tetrahedral alkoxide is protonated
氰醇
Cyanohydrin
年表Timeline
- 1832
维勒与李比希研究苯甲醛与氰化物（安息香）
Wöhler and Liebig study benzaldehyde with cyanide (benzoin)
- 1973
伯吉与邓尼茨提出进攻角
Bürgi and Dunitz describe the attack angle