定义Definition
弯箭头（电子推移箭头）是书写反应机理时表示电子移动的符号。双钩弯箭头表示一对电子的移动，单钩（鱼钩）箭头表示单个电子的移动。箭头从电子的来源（孤电子对或化学键）出发，指向电子的去处（原子或新形成的键）。
Curly arrows (arrow pushing) show electron movement in reaction mechanisms. A full-headed arrow shows a pair of electrons moving, and a half-headed (fish-hook) arrow a single electron. The arrow starts at the source of the electrons, a lone pair or a bond, and ends where they go, an atom or the position of a new bond.
书写规则Rules
① 箭头尾部必须在孤电子对或键上，不能从原子核或正电荷出发；② 指向原子表示电子对到该原子上，指向两原子之间表示形成新键；③ 每一步前后电荷总数守恒；④ 碳原子不能超过四根键。
1. The tail must start on a lone pair or a bond, never on a nucleus or a positive charge. 2. Ending on an atom means the pair goes to that atom; ending between two atoms means a new bond forms. 3. Total charge is conserved at every step. 4. Carbon must never have more than four bonds.
例：卤代烃的水解Example: hydrolysis of a halogenoalkane
SN2 中画两个箭头：一个从 OH⁻ 的孤电子对指向 δ+ 碳，另一个从 C–Br 键指向 Br，Br⁻ 带着电子对离去。
In SN2 two arrows are drawn: one from a lone pair of OH⁻ to the δ+ carbon, and one from the C–Br bond to the bromine, which leaves as Br⁻ with the pair.
年表Timeline
- 1922
罗宾逊等开始用弯箭头表示电子转移
Robinson and co-workers begin using curved arrows to show electron movement