Organic Nitrogen Compounds: Amines, Amides and Amino Acids | 有机含氮化合物：胺、酰胺与氨基酸

📚 Organic Nitrogen Compounds: Amines, Amides and Amino Acids | 有机含氮化合物：胺、酰胺与氨基酸

Organic nitrogen compounds dominate many areas of chemistry, from laboratory synthesis to the structure of living systems. This article focuses on the A-level core families: amines, amides, amino acids and proteins. Understanding the lone pair on nitrogen, the geometry of the amino group, and the stability of the amide link allows you to predict reactions such as base formation, nucleophilic substitution, condensation and hydrolysis.

有机含氮化合物在从实验室合成到生命系统结构的许多化学领域中都占据主导地位。本文聚焦 A-level 核心类别：胺、酰胺、氨基酸和蛋白质。理解氮原子上的孤对电子、氨基的几何构型以及酰胺键的稳定性，可以帮助你预测成碱、亲核取代、缩合和水解等反应。

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1. Families of Organic Nitrogen Compounds | 有机含氮化合物的分类

Amines are derivatives of ammonia in which one or more hydrogen atoms have been replaced by alkyl or aryl groups. They are classified as primary (RNH₂), secondary (R₂NH) or tertiary (R₃N) according to the number of carbon-containing groups attached to nitrogen. Amides contain the acyl group C=O bonded to nitrogen, giving the functional group RCONH₂ for primary amides. Amino acids contain both an amino group and a carboxylic acid group, while proteins are natural polyamides formed from amino acid monomers.

胺是氨中的一个或多个氢原子被烷基或芳基取代后的衍生物。根据连接在氮原子上的含碳基团数目，胺可分为伯胺（RNH₂）、仲胺（R₂NH）和叔胺（R₃N）。酰胺含有与氮原子相连的酰基 C=O，伯酰胺的官能团为 RCONH₂。氨基酸同时含有氨基和羧基，而蛋白质是由氨基酸单体形成的天然聚酰胺。

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2. Naming Amines and Amides | 胺和酰胺的命名

Simple primary amines are named by adding the suffix -amine to the alkyl group name: CH₃NH₂ is methylamine and CH₃CH₂NH₂ is ethylamine. For secondary and tertiary amines, the longest carbon chain is the parent and N- prefixes identify the groups attached to nitrogen. Amides are named after the parent carboxylic acid by replacing -oic acid with -amide. Thus ethanoic acid gives ethanamide, CH₃CONH₂. N-substituted amides use N-alkyl prefixes on the nitrogen atom.

简单的伯胺通过在烷基名称后加上后缀“-胺”来命名：CH₃NH₂ 是甲胺，CH₃CH₂NH₂ 是乙胺。仲胺和叔胺以最长碳链为母体，并用 N- 前缀标明连接在氮原子上的基团。酰胺的命名是把母体羧酸的 -oic acid 替换为 -amide 得到。因此乙酸（ethanoic acid）对应乙酰胺（ethanamide），即 CH₃CONH₂。N-取代酰胺在氮原子上使用 N- 烷基前缀。

Formula	IUPAC name	中文名
CH₃NH₂	methylamine	甲胺
CH₃CH₂NH₂	ethylamine	乙胺
(CH₃CH₂)₂NH	diethylamine	二乙胺
CH₃CONH₂	ethanamide	乙酰胺
CH₃CONHCH₃	N-methylethanamide	N-甲基乙酰胺

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3. Structure and Basicity of Amines | 胺的结构与碱性

The nitrogen atom in an amine is sp³ hybridised, giving a trigonal pyramidal arrangement around nitrogen with a lone pair occupying one position. This lone pair can accept a proton, so amines are Brønsted–Lowry bases. In water, a primary amine establishes an equilibrium:

胺中的氮原子为 sp³ 杂化，氮周围呈三角锥形排列，其中一个位置被孤对电子占据。该孤对电子可以接受质子，因此胺是 Brønsted–Lowry 碱。在水中，伯胺建立如下平衡：

RNH₂ + H₂O ⇌ RNH₃⁺ + OH⁻

Aliphatic amines are generally stronger bases than ammonia because electron-donating alkyl groups push electron density towards the nitrogen atom. Phenylamine, C₆H₅NH₂, is much weaker because the nitrogen lone pair is delocalised into the benzene ring, making it less available to accept a proton. Basicity can be compared using pKb values or by measuring the pH of equimolar solutions.

脂肪胺通常比氨更强的碱，因为给电子的烷基会把电子密度推向氮原子。苯胺（C₆H₅NH₂）则弱得多，因为氮上的孤对电子离域进入苯环，使其接受质子的能力降低。碱性可以用 pKb 值或等浓度溶液的 pH 进行比较。

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4. Preparation of Amines | 胺的制备

A common laboratory preparation is the nucleophilic substitution of a halogenoalkane with excess ammonia. The excess ammonia reduces further substitution, although some secondary and tertiary amines can still form:

一种常见的实验室制备方法是卤代烷与过量氨的亲核取代反应。过量氨可以减少进一步取代，但仍可能生成一些仲胺和叔胺：

CH₃CH₂Br + 2NH₃ → CH₃CH₂NH₂ + NH₄Br

Nitriles can be reduced to primary amines using lithium aluminium hydride in dry ether or by catalytic hydrogenation. This is useful because it extends the carbon chain by one carbon atom:

腈可以在干乙醚中用氢化铝锂还原，或通过催化加氢还原成伯胺。该方法很有用，因为它能使碳链延长一个碳原子：

R–C≡N + 2H₂ → R–CH₂NH₂

Aromatic amines such as phenylamine are prepared by reducing nitrobenzene with tin and concentrated hydrochloric acid, followed by addition of sodium hydroxide:

芳香胺（如苯胺）可通过锡和浓盐酸还原硝基苯，然后加入氢氧化钠来制备：

C₆H₅NO₂ + 6[H] → C₆H₅NH₂ + 2H₂O

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5. Reactions of Amines as Bases and Nucleophiles | 胺作为碱和亲核试剂的反应

Amines react with acids to form soluble ammonium salts. For example, methylamine reacts with hydrochloric acid to form methylammonium chloride:

胺与酸反应生成可溶的铵盐。例如，甲胺与盐酸反应生成氯化甲铵：

CH₃NH₂ + HCl → CH₃NH₃⁺Cl⁻

Because the amine nitrogen carries a lone pair, amines also act as nucleophiles. With halogenoalkanes, primary amines can undergo further alkylation to secondary amines, tertiary amines and finally quaternary ammonium salts. With acyl chlorides or acid anhydrides, primary amines form N-substituted amides:

由于胺的氮原子上带有孤对电子，胺也可以作为亲核试剂。与卤代烷反应时，伯胺可继续烷基化，依次生成仲胺、叔胺，最终生成季铵盐。与酰氯或酸酐反应时，伯胺生成 N-取代酰胺：

RNH₂ + R’COCl → R’CONHR + HCl

Phenylamine can also react with nitrous acid at low temperature to form a diazonium salt. This intermediate is important in the synthesis of azo dyes, although it is unstable and must be kept cold.

苯胺在低温下还能与亚硝酸反应生成重氮盐。该中间体在偶氮染料合成中非常重要，但它不稳定，必须保持在低温下。

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6. Amides: Formation and Hydrolysis | 酰胺：生成与水解

Amides are formed when acyl chlorides react with ammonia or amines. The reaction is vigorous and produces an amide plus hydrogen chloride, which is usually neutralised by

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