Functional Groups | 官能团

📚 Functional Groups | 官能团

In organic chemistry, the behaviour of a molecule is not determined mainly by the length of its carbon chain, but by the small reactive part of the molecule called the functional group. A functional group is an atom or group of atoms that gives an organic compound its characteristic chemical properties and reactions.

在有机化学中，分子的化学行为主要不是由碳链长度决定，而是由分子中较小的活性部分——官能团决定。官能团是赋予有机化合物特征化学性质和反应的一个原子或原子团。

This article covers the functional groups required for Cambridge International A Level Chemistry. You will learn how to recognise each group, name representative compounds, and predict typical reactions.

本文涵盖剑桥国际 A Level 化学要求掌握的官能团。你将学习如何识别每个官能团、命名代表性化合物并预测典型反应。

1. What Are Functional Groups? | 什么是官能团？

A functional group is the reactive site within an organic molecule. Compounds that contain the same functional group are members of the same homologous series and show similar chemical behaviour.

官能团是有机分子中的反应部位。含有相同官能团的化合物属于同一同系物，并表现出相似的化学行为。

For example, ethanol (CH₃CH₂OH) and propan-1-ol (CH₃CH₂CH₂OH) both contain the hydroxyl group –OH. They both react with sodium, carboxylic acids and oxidising agents in the same way because the functional group is the same.

例如，乙醇 (CH₃CH₂OH) 和丙-1-醇 (CH₃CH₂CH₂OH) 都含有羟基 –OH。由于官能团相同，它们与钠、羧酸和氧化剂的反应方式相同。

In the Cambridge A Level specification, organic chemistry is organised around the reactions of common functional groups such as alkenes, halogenoalkanes, alcohols, carbonyl compounds, carboxylic acids and nitrogen compounds.

在剑桥 A Level 大纲中，有机化学围绕烯烃、卤代烷、醇、羰基化合物、羧酸和含氮化合物等常见官能团的反应展开。

2. Alkenes: The C=C Double Bond | 烯烃：碳碳双键

Alkenes contain the carbon–carbon double bond C=C as their functional group. The double bond is a region of high electron density, so alkenes mainly undergo electrophilic addition reactions.

烯烃的官能团是碳碳双键 C=C。双键是电子密度较高的区域，因此烯烃主要发生亲电加成反应。

For example, ethene reacts with hydrogen bromide to form bromoethane by electrophilic addition:

例如，乙烯与溴化氢发生亲电加成反应生成溴乙烷：

CH₂=CH₂ + HBr → CH₃CH₂Br

When an unsymmetrical alkene is used, the major product follows Markovnikov’s rule: the hydrogen atom adds to the carbon that already has more hydrogen atoms.

当使用不对称烯烃时，主要产物遵循马氏规则：氢原子加到已有更多氢原子的碳上。

Alkenes also decolourise bromine water. This reaction is used as a simple test for unsaturation.

烯烃还能使溴水褪色。该反应可用作检验不饱和性的简单方法。

3. Halogenoalkanes: The C–X Bond | 卤代烷：碳卤键

Halogenoalkanes contain a polar carbon–halogen bond, written C–X, where X = F, Cl, Br or I. The carbon atom carries a partial positive charge and can be attacked by nucleophiles.

卤代烷含有极性的碳卤键，写作 C–X，其中 X = F、Cl、Br 或 I。碳原子带有部分正电荷，可被亲核试剂进攻。

With aqueous sodium hydroxide, a halogenoalkane undergoes nucleophilic substitution to form an alcohol:

与氢氧化钠水溶液反应时，卤代烷发生亲核取代生成醇：

CH₃CH₂Br + NaOH → CH₃CH₂OH + NaBr

With hot ethanolic potassium hydroxide, elimination takes place instead, producing an alkene:

与热的氢氧化钾乙醇溶液反应时，则发生消除反应，生成烯烃：

CH₃CH₂Br + KOH → CH₂=CH₂ + KBr + H₂O

The relative rates of hydrolysis of different halogenoalkanes can be tested using aqueous silver nitrate. The C–I bond is the weakest carbon–halogen bond, so iodoalkanes react fastest.

不同卤代烷的水解速率可用硝酸银水溶液检验。C–I 键是最弱的碳卤键，因此碘代烷反应最快。

4. Alcohols: The Hydroxyl Group | 醇：羟基

Alcohols contain the hydroxyl group –OH attached to a saturated carbon atom. Primary and secondary alcohols can be oxidised, but tertiary alcohols are not easily oxidised under mild conditions.

醇含有连接在饱和碳原子上的羟基 –OH。伯醇和仲醇可被氧化，而叔醇在温和条件下不易被氧化。

Primary alcohols are oxidised first to aldehydes and then to carboxylic acids. Ethanol is oxidised by acidified potassium dichromate(VI), which changes colour from orange to green:

伯醇先被氧化为醛，再被氧化为羧酸。乙醇可被酸化重铬酸钾(VI)氧化，溶液由橙色变为绿色：

CH₃CH₂OH + [O] → CH₃CHO + H₂O

CH₃CHO + [O] → CH₃COOH

Alcohols also undergo esterification with carboxylic acids and can be dehydrated to alkenes using hot concentrated sulfuric acid or an aluminium oxide catalyst.

醇还能与羧酸发生酯化反应，并可在热的浓硫酸或氧化铝催化剂作用下脱水生成烯烃。

5. Aldehydes and Ketones: The Carbonyl Group | 醛和酮：羰基

Aldehydes and ketones both contain the carbonyl group C=O. In an aldehyde, the carbonyl group is at the end of the carbon chain and is attached to at least one hydrogen atom. In a ketone, the carbonyl group is attached to two carbon atoms.

醛和酮都含有羰基 C=O。在醛中，羰基位于碳链末端，并至少与一个氢原子相连。在酮中，羰基与两个碳原子相连。

Aldehydes are easily oxidised to carboxylic acids, whereas ketones resist oxidation under the same conditions. This difference is used in Fehling’s and Tollens’ tests, where aldehydes give positive results but ketones do not.

醛容易被氧化成羧酸，而酮在相同条件下不易被氧化。这一差异可用于费林试剂和托伦试剂检验：醛给出阳性结果，而酮不能。

Both aldehydes and ketones can be reduced to alcohols using sodium borohydride, NaBH₄, or lithium aluminium hydride, LiAlH₄:

醛和酮都可以用硼氢化钠 (NaBH₄) 或氢化铝锂 (LiAlH₄) 还原为醇：

CH₃CHO + 2[H] → CH₃CH₂OH

CH₃COCH₃ + 2[H] → CH₃CH(OH)CH₃

6. Carboxylic Acids: The Carboxyl Group | 羧酸：羧基

Carboxylic acids contain the carboxyl group –COOH. The carboxyl group consists of a carbonyl group and a hydroxyl group attached to the same carbon atom. Carboxylic acids are weak acids in water.

羧酸含有羧基 –COOH。羧基由连接在同一碳原子上的羰

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Functional Groups | 官能团