定义Definition
腈是含氰基 –C≡N 的有机化合物，通式 R–C≡N，如乙腈 CH₃CN、丙腈 CH₃CH₂CN。腈可由卤代烃与氰化物反应或由醛酮与 HCN 加成得到，能水解为羧酸或还原为伯胺，是在合成中增长碳链的重要中间体。
A nitrile is an organic compound containing the –C≡N group, general formula R–C≡N, such as ethanenitrile (CH₃CN) and propanenitrile (CH₃CH₂CN). Nitriles are made from halogenoalkanes and cyanide or by adding HCN to aldehydes and ketones; they hydrolyse to carboxylic acids or reduce to primary amines, making them key intermediates for lengthening carbon chains.
制备：碳链增长一个碳Preparation, adding one carbon
卤代烃与 KCN 的乙醇溶液加热回流，发生亲核取代：CH₃CH₂Br + CN⁻ → CH₃CH₂CN + Br⁻。命名时氰基碳计入主链，所以溴乙烷得到的是丙腈。
Heat a halogenoalkane under reflux with KCN in ethanol for nucleophilic substitution: CH₃CH₂Br + CN⁻ → CH₃CH₂CN + Br⁻. The nitrile carbon counts in the name, so bromoethane gives propanenitrile.
水解与还原Hydrolysis and reduction
与稀酸加热回流水解为羧酸：CH₃CH₂CN + 2H₂O + H⁺ → CH₃CH₂COOH + NH₄⁺；用 LiAlH₄ 或 H₂/Ni 还原为伯胺：CH₃CH₂CN + 4[H] → CH₃CH₂CH₂NH₂。
Heating under reflux with dilute acid hydrolyses a nitrile to a carboxylic acid: CH₃CH₂CN + 2H₂O + H⁺ → CH₃CH₂COOH + NH₄⁺. LiAlH₄ or H₂ over nickel reduces it to a primary amine: CH₃CH₂CN + 4[H] → CH₃CH₂CH₂NH₂.
结构与谱学Structure and spectra
氰基碳为 sp 杂化，C–C≡N 呈直线形。红外光谱在约 2200–2260 cm⁻¹ 有 C≡N 伸缩振动的特征吸收。
The nitrile carbon is sp hybridised and C–C≡N is linear. In infrared spectra the C≡N stretch absorbs characteristically at about 2200–2260 cm⁻¹.