定义Definition
E1 反应是单分子消除：底物先解离生成碳正离子（决速步），然后溶剂或弱碱夺取 β-H 生成烯烃。速率只与底物浓度有关。
The E1 reaction is unimolecular elimination: the substrate ionises to a carbocation (rate-determining), then solvent or a weak base removes a β-H to form the alkene. The rate depends only on substrate concentration.
特征Characteristics
与 SN1 共用碳正离子中间体，二者常同时发生，升温有利于 E1（熵增）。一级动力学；叔 > 仲；产物以扎伊采夫烯烃为主；碳正离子可重排；无立体专一要求（不需要反式共平面），通常得到较稳定的 E 烯烃。
It shares the carbocation with SN1 and the two usually compete, with heat favouring E1 (entropy). First order; 3° > 2°; mainly Zaitsev alkenes; rearrangements possible; no anti-periplanar requirement, typically giving the more stable E-alkene.
醇的酸催化脱水Acid-catalysed alcohol dehydration
叔、仲醇在浓硫酸或磷酸中加热脱水是 E1 的典型例子：羟基质子化后以水离去，碳正离子失去质子。
Heating tertiary or secondary alcohols with concentrated H₂SO₄ or H₃PO₄ is a classic E1: the protonated hydroxyl leaves as water and the cation loses a proton.
动力学同位素效应Kinetic isotope effect
β-H 换成 D 时 E1 速率几乎不变（C–H 断裂不在决速步），而 E2 有明显一级同位素效应，可据此区分机理。
Deuterating the β-H barely changes E1 rates (C–H breaking is not rate-determining), whereas E2 shows a primary KIE — a mechanistic test.
反应Reactions
叔底物、极性质子溶剂、加热、弱碱
Tertiary substrates, polar protic solvents, heat, weak bases
离去基团离去生成碳正离子（决速）。
Ionisation to the carbocation (rate-determining).
（可能重排。）
(Possible rearrangement.)
β-H 被夺走形成双键。
β-H removal forms the double bond.
叔丁醇脱水得异丁烯。
tert-Butanol dehydrates to isobutene.
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.
离去基团先离去，生成碳正离子
The leaving group departs first, giving a carbocation
弱碱（水）夺去 β-H，电子对形成 π 键
A weak base removes a β-H; its electrons form the π bond
2-甲基丙烯（扎伊采夫产物）
2-Methylpropene (Zaitsev product)
年表Timeline
- 1940s
休斯与英戈尔德阐明 E1 机理
Hughes and Ingold describe the E1 mechanism