📚 Functional Groups in Organic Chemistry | 有机化学官能团
Functional groups are specific atoms or groups of atoms within organic molecules that determine the characteristic chemical reactivity and physical properties of those compounds. In A-Level Chemistry, a thorough understanding of functional groups is essential for predicting reactions, drawing isomers, and systematically naming organic compounds according to IUPAC rules. Mastering functional groups allows you to see the 'behaviour' of a molecule beyond its carbon skeleton.
官能团是有机分子中决定其化学特征反应和物理性质的特定原子或原子团。在A-Level化学中，深入理解官能团对于预测反应、绘制异构体以及根据IUPAC规则系统命名有机化合物至关重要。掌握官能团能让您透过碳骨架，看懂分子的“行为举止”。
1. What Are Functional Groups? | 什么是官能团？
In organic chemistry, a functional group is a specific arrangement of atoms that gives a molecule its distinctive chemical properties. The rest of the molecule, typically a hydrocarbon chain or ring, provides a framework but contributes less to the reactivity. For example, all alcohols contain the hydroxyl group (–OH) and undergo similar reactions such as dehydration or esterification, regardless of the length of the carbon chain.
在有机化学中，官能团是一种特定的原子排列方式，赋予分子独特的化学性质。分子的其余部分通常是碳氢链或环，提供骨架但对反应性的贡献较小。例如，所有醇都含有羟基（–OH），无论碳链长短，都会发生类似的脱水或酯化反应。
Functional groups can be classified into different families: hydrocarbons with multiple bonds (alkenes, alkynes), halogen-containing compounds, oxygen-based groups (alcohols, ethers, carbonyls, carboxyls, esters), and nitrogen-based groups (amines, amides, nitriles, nitro). The presence of a functional group is denoted by a prefix or suffix when naming the compound.
官能团可以划分为不同家族：含重键的烃（烯烃、炔烃）、含卤化合物、含氧基团（醇、醚、羰基、羧基、酯）以及含氮基团（胺、酰胺、腈、硝基）。在命名化合物时，通过前缀或后缀来表示官能团的存在。
2. Alkanes and Alkyl Groups | 烷烃与烷基
Alkanes are saturated hydrocarbons with only C–C and C–H single bonds. They contain no functional group as such, but the alkyl groups derived from alkanes act as substituents in more complex molecules. Examples of alkyl groups include methyl (–CH₃), ethyl (–C₂H₅), propyl (–C₃H₇), and butyl (–C₄H₉). Branched alkyl groups are also common, such as isopropyl ((CH₃)₂CH–).
烷烃是只含C–C和C–H单键的饱和烃。它们本身不含官能团，但从烷烃衍生出的烷基在更复杂的分子中用作取代基。常见的烷基包括甲基（–CH₃）、乙基（–C₂H₅）、丙基（–C₃H₇）和丁基（–C₄H₉）。支链烷基也很普遍，如异丙基（(CH₃)₂CH–）。
In IUPAC nomenclature, alkanes form the stem of the name, and alkyl branches are listed as prefixes in alphabetical order with their position numbers. For example, 2-methylpentane has a methyl group attached to the second carbon of a five-carbon parent chain. Although alkanes are relatively unreactive, they undergo combustion and free-radical substitution with halogens.
在IUPAC命名中，烷烃构成名称的词干，烷基支链按字母顺序与前缀位置号一起列出。例如，2-甲基戊烷表示一个甲基连接在五碳主链的第二个碳上。尽管烷烃相对不活泼，但它们能燃烧并与卤素发生自由基取代反应。
3. Alkenes: The C=C Double Bond | 烯烃：C=C双键
The functional group of alkenes is the carbon– round the double bond is trigonal planar with a bond angle of about 120°. The presence of the C=C bond is indicated by the suffix '-ene' and the stereochemistry can give rise to geometrical isomers (cis/trans or E/Z).
烯烃的官能团是碳碳双键（C=C）。这种不饱和键由一个σ键和一个π键组成，使烯烃比烷烃活泼得多。双键周围的几何构型为平面三角形，键角约为120°。C=C键的存在用后缀“-烯”表示，且立体化学可产生几何异构体（顺反或E/Z）。
Alkenes undergo electrophilic addition reactions, where the π electrons attack an electrophile such as HBr, Br₂, or H₂O (with acid catalyst). Polymerisation is also a key reaction, forming long-chain polymers like poly(ethene). The position of the double bond is indicated by the lowest possible number in the carbon chain, e.g. but-1-ene versus but-2-ene.
烯烃发生亲电加成反应，π电子进攻亲电试剂如HBr、Br₂或H₂O（酸催化）。聚合也是一类重要反应，生成聚烯烃等长链高分子。双键位置用碳链中尽可能小的数字标出，例如丁-1-烯与丁-2-烯。
4. Halogenoalkanes: C–X Bond | 卤代烷：C–X键
Halogenoalkanes contain a halogen atom (F, Cl, Br, or I) bonded to a saturated carbon. The functional group is the polar carbon–halogen bond, which makes the compounds susceptible to nucleophilic substitution and elimination reactions. The naming uses the prefixes fluoro-, chloro-, bromo-, and iodo- with appropriate numbers.
卤代烷含有一个结合在饱和碳上的卤素原子（F, Cl, Br或I）。其官能团是极性的碳-卤键，这使得化合物容易发生亲核取代和消除反应。命名时使用前缀氟-、氯-、溴-、碘-并标注相应数字。
Reactivity increases down the halogen group because the C–X bond energy decreases. Nucleophiles such as OH⁻, CN⁻, and NH₃ can replace the halogen, forming alcohols, nitriles, or amines. Alternatively, hot ethanolic hydroxide induces elimination to form alkenes. The chemical behaviour is strongly influenced by whether the halogenoalkane is primary, secondary, or tertiary.
由于C–X键能降低，反应活性沿卤素族自上而下增强。亲核试剂如OH⁻、CN⁻和NH₃可取代卤原子，生成醇、腈或胺。另一方面，热的氢氧化钾乙醇溶液引发消除反应生成烯烃。化学行为受卤代烷是一级、二级还是三级的影响很大。
5. Alcohols: The Hydroxyl Group –OH | 醇：羟基–OH
The hydroxyl functional group (–OH) attached to a saturated carbon defines the alcohol family. Alcohols are classified as primary, secondary, or tertiary based on the carbon holding the –OH. The suffix is '-ol', often with the number indicating the position of the hydroxyl group, e.g. ethanol, propan-1-ol, propan-2-ol.
连接在饱和碳上的羟基官能团（–OH）定义了醇族化合物。根据承载–OH的碳的级数，醇被划分为一级、二级或三级醇。其名称后缀为“-醇”，并常带数字标示羟基位置，如乙醇、丙-1-醇、丙-2-醇。
Alcohols are polar and can form hydrogen bonds, giving them relatively high boiling points and good solubility in water. Chemically, they undergo combustion, oxidation (to aldehydes, ketones, or carboxylic acids), esterification, and substitution to halogenoalkanes. The –OH group can also be deprotonated by reactive metals to give alkoxide ions.
醇是极性的，能形成氢键，使其沸点较高、水溶性好。化学上，醇可燃烧、被氧化（成醛、酮或羧酸）、酯化，以及被取代生成卤代烷。–OH基团还可被活泼金属脱去质子，形成醇盐离子。
6. Carbonyl Compounds: Aldehydes and Ketones | 羰基化合物：醛与酮
olar functional group in which the carbon is sp² hybridised. Aldehydes have the carbonyl group at the end of a carbon chain (with at least one hydrogen attached), and are named with the suffix '-al' anal, ethanal. Ketones have the carbonyl group on a non-terminal carbon and use the suffix '-one', e.g. propanone.
羰基（C=O）是强极性官能团，其中碳为sp²杂化。醛的羰基位于碳链末端（至少连有一个氢），命名后缀用“-醛”，如甲醛、乙醛。酮的羰基在非末端碳上，后缀用“-酮”，如丙酮（丙-2-酮）。
idised to carboxylic acids, while ketones resist oxidation. This difference allows Fehling's or Tollens' reagent to distinguish between them. The polarity of C=O also enables the formation of 2,4-DNPH derivatives for identification.
羰基化合物发生亲核加成，可使用HCN或2,4-二硝基苯肼等试剂。醛易被氧化为羧酸，而酮则不易被氧化。这一差异可用费林试剂或托伦斯试剂区分。C=O的极性还可使其生成2,4-二硝基苯腙衍生物用于鉴定。
7. Carboxylic Acids: The Carboxyl Group –COOH | 羧酸：羧基–COOH
The carboxyl functional group consists of a carbonyl and a hydroxyl on the same carbon (–COOH). This acidic group donates a proton in water, giving carboxylic acids their characteristic weak acidity. The suffix is '-oic acid', and the carbon of the –COOH is always numbered as carbon 1. Examples include methanoic acid and ethanoic acid.
羧基官能团由同一个碳上的羰基和羟基组成（–COOH）。这个酸性基团在水中释放质子，使羧酸呈现特征的弱酸性。后缀为“-酸”，且–COOH的碳总是编号为1。实例包括甲酸和乙酸。
Carboxylic acids react with metals, bases, carbonates, and alcohols (esterification). They can be reduced to primary alcohols by LiAlH₄, and converted into derivatives such as acyl chlorides, esters, and amides. The –COOH group is strongly hydrogen-bonded, leading to high boiling points and dimer formation in non-polar solvents.
羧酸与金属、碱、碳酸盐以及醇（酯化）反应。它们可被LiAlH₄还原为一级醇，并可转化为酰氯、酯和酰胺等衍生物。–COOH基团能形成强氢键，导致沸点较高，在非极性溶剂中常形成二聚体。
8. Esters: The –COOR Linkage | 酯：–COOR键合
Esters contain the functional group –COOR, where R is an alkyl or aryl group. They are derived from carboxylic acids by replacing the –OH with an –OR group. The name of an ester comes from the alcohol and the carboxylic acid, e.g. methyl ethanoate from methanol and ethanoic acid. The suffix is '-oate'.
酯含有官能团–COOR，其中R为烷基或芳基。它们由羧酸中的–OH被–OR基团取代而生成。酯的名称由醇和羧酸组合而成，例如醋酸甲酯（乙酸甲酯）由甲醇和乙酸制得。后缀为“-酸酯”。
Esters are often sweet-smelling and are used as solvents and flavourings. Chemically, they undergo hydrolysis (both acidic and alkaline) to regenerate the parent acid and alcohol. Alkaline hydrolysis yields the carboxylate salt. Transesterification swaps the alcohol part, making esters important in biodiesel production.
酯通常有芳香气味，常用作溶剂和香料。化学上，酯发生水解（酸性或碱性）重新生成母体酸和醇。碱性水解得到羧酸盐。酯交换反应可调换醇的部分，使酯在生物柴油生产中十分重要。
9. Acyl Chlorides and Acid Anhydrides | 酰氯与酸酐
Acyl chlorides (R–COCl) and acid anhydrides ((RCO)₂O) are reactive carboxylic acid derivatives. They share the acyl group (RCO–) bonded to a good leaving group (Cl⁻ or RCOO⁻). Acyl chlorides are named with the suffix '-oyl chloride', e.g. ethanoyl chloride. Acid anhydrides are named by replacing 'acid' with 'anhydride'.
酰氯（R–COCl）和酸酐（(RCO)₂O）是活泼的羧酸衍生物。它们都含有一个与良好离去基团（Cl⁻或RCOO⁻）相连的酰基（RCO–）。酰氯以后缀“-酰氯”命名，如乙酰氯。酸酐则将“酸”替换为“酐”来命名。
These compounds react vigorously with water, alcohols, ammonia, and amines to produce carboxylic acids, esters, amides, and substituted amides respectively. The reactions are nucleophilic addition–elimination. Acyl chlorides are more reactive than acid anhydrides, but both are widely used in organic synthesis to introduce the acyl group.
这类化合物与水、醇、氨和胺剧烈反应，分别生成羧酸、酯、酰胺和N-取代酰胺。反应机理为亲核加成–消除。酰氯比酸酐更活泼，但两者在有机合成中广泛用于引入酰基。
10. Amines and Nitro Compounds | 胺与硝基化合物
Amines contain the amino group –NH₂, –NHR, or –NR₂. They are derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. Primary amines are named with the suffix '-amine' or the prefix 'amino-', e.g. ethylamine, phenylamine. Amines are basic and can act as nucleophiles.
胺含有氨基–NH₂、–NHR或–NR₂。它们由氨中的一个或多个氢原子被烷基或芳基取代而得到。一级胺以后缀“-胺”或前缀“氨基-”命名，如乙胺、苯胺。胺具有碱性并可充当亲核试剂。
Nitro compounds possess the nitro group –NO₂, often attached directly to a benzene ring, as in nitrobenzene. The nitro group is named as the prefix 'nitro-'. Nitroarenes are reduced to amines using tin and concentrated HCl, providing a route to aromatic amines. The –NO₂ group is electron-withdrawing and deactivates the benzene ring towards electrophilic substitution.
硝基化合物含有硝基–NO₂，通常直接连在苯环上，如硝基苯。硝基以前缀“硝基-”命名。硝基芳烃可用锡和浓盐酸还原为胺，是制备芳香胺的一种途径。–NO₂基团是吸电子基，使苯环对亲电取代反应钝化。
11. Amides and Nitriles | 酰胺与腈
The amide functional group is –CONH₂ (or substituted variations). Primary amides are named by replacing the '-oic acid' suffix with '-amide', e.g. ethanamide. Amides are neutral and can be prepared by the reaction of acyl chlorides with ammonia. They have high boiling points due to hydrogen bonding.
酰胺官能团是–CONH₂（或取代形式）。一级酰胺的命名将“-酸”后缀改为“-酰胺”，如乙酰胺。酰胺为中性，可通过酰氯与氨反应制备。因氢键作用，酰胺沸点较高。
Nitriles contain the cyano group –C≡N. They are named with the suffix '-nitrile' or the prefix 'cyano-', e.g. ethanenitrile. Nitriles are formed by nucleophilic substitution of halogenoalkanes with cyanide ions. Hydrolysis of nitriles yields carboxylic acids, and reduction with LiAlH₄ gives primary amines, making them versatile intermediates.
腈含有氰基–C≡N。命名时用后缀“-腈”或前缀“氰基-”，如乙腈。腈可由卤代烷与氰离子亲核取代制得。腈水解生成羧酸，被LiAlH₄还原可得一级胺，这使腈成为用途广泛的中间体。
12. Summary: Functional Group Priority in Naming | 总结：命名中的官能团优先级
When a molecule contains more than one functional group, IUPAC rules assign a priority order to decide which group is the principal function (given as the suffix) and which are treated as substituents (given as prefixes). The table below summarises the decreasing order of priority for common groups in A-Level Chemistry.
当分子含有多个官能团时，IUPAC规则规定了优先级顺序，以确定哪个基团为主要官能团（作为后缀）以及哪些基团作为取代基（前缀）。下表总结了A-Level化学中常见基团递减的优先顺序。
Priority: –COOH > –COOR > –COCl > –CONH₂ > –CN > –CHO > >C=O > –OH > –NH₂ > C=C > –X > –NO₂, alkyl
优先级：–COOH > –COOR > –COCl > –CONH₂ > –CN > –CHO > >C=O > –OH > –NH₂ > C=C > –X > –NO₂, 烷基
| Functional Group | Suffix | Prefix |
|---|---|---|
| Carboxylic acid –COOH | -oic acid | - |
| Ester –COOR | -oate | - |
| Acyl chloride –COCl | -oyl chloride | - |
| Amide –CONH₂ | -amide | - |
| Nitrile –CN | -nitrile | cyano- |
| Aldehyde –CHO | -al | formyl- |
| Ketone >C=O | -one | oxo- |
| Alcohol –OH | -ol | hydroxy- |
| Amine –NH₂ | -amine | amino- |
| Alkene C=C | -ene | - |
| Halogenoalkane –X | - | fluoro-, chloro- etc. |
For compounds with multiple functional groups, the principal group determines the suffix and the numbering of the carbon chain. Other groups become prefixes listed in alphabetical order (ignoring di-, tri-). For example, 3-hydroxybutanoic acid has –OH as a prefix and –COOH as the suffix. Mastering this priority order is essential for correct systematic nomenclature in Cambridge A-Level examinations.
对于含有多个官能团的化合物，主要基团决定后缀和碳链的编号。其它基团作为前缀，按字母顺序列出（忽略二、三等）。例如，3-羟基丁酸中，–OH为前缀，–COOH为后缀。掌握这一优先顺序对剑桥A-Level考试中正确系统命名至关重要。
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