📚 Edexcel A Level Chemistry Topic 17: Carbonyl Compounds, Carboxylic Acids and Derivatives | 爱德思A-Level化学 第17章：羰基化合物、羧酸及其衍生物
This topic brings together the reactivity of the carbonyl group, C=O, which appears in aldehydes, ketones, carboxylic acids, esters, acyl chlorides and condensation polymers. For Edexcel A-Level Chemistry, Topic 17 is a major area of organic chemistry that tests your understanding of structure, mechanism, isomerism and practical identification. The key idea is that the polarised carbon–oxygen double bond makes the carbonyl carbon electron-deficient and open to attack by nucleophiles.
本主题将羰基 C=O 的反应性串联起来，它出现在醛、酮、羧酸、酯、酰氯和缩合聚合物中。对 Edexcel A-Level 化学来说，第17章是有机化学的重要板块，考查结构、反应机理、异构现象和实验鉴别。核心思想是极化的碳氧双键使羰基碳缺电子，容易受到亲核试剂的进攻。
1. The Carbonyl Group: Structure and Polarity | 羰基：结构与极性
The carbonyl group consists of a carbon atom double-bonded to an oxygen atom. The C=O bond is polar because oxygen is more electronegative than carbon, so the carbon carries a partial positive charge (δ+) and the oxygen carries a partial negative charge (δ-). The three groups around the carbonyl carbon are arranged in a trigonal planar shape with bond angles of about 120°.
羰基由碳原子与氧原子双键连接而成。由于氧的电负性比碳强，C=O 键是极性键，碳带部分正电荷 δ+，氧带部分负电荷 δ-。羰基碳周围的三组基团呈平面三角形排列，键角约为 120°。
This polarity is the foundation of carbonyl chemistry. The electron-deficient carbon is attacked by nucleophiles such as cyanide ions, hydride ions and ammonia derivatives. The oxygen atom can be protonated in acid-catalysed reactions, which makes the carbon even more positive and speeds up nucleophilic attack.
这种极性是羰基化学的基础。缺电子的碳会被氰根离子、氢负离子和氨的衍生物等亲核试剂进攻。氧原子可在酸催化反应中被质子化，使碳更显正电，从而加快亲核进攻。
2. Naming and Physical Properties | 命名与物理性质
Aldehydes end in -al and contain the carbonyl group at the end of a carbon chain, for example ethanal, CH₃CHO. Ketones end in -one and have the carbonyl group within the chain, for example propanone, CH₃COCH₃. The carbonyl carbon is always assigned the lowest possible locant in the chain.
醛的英文名以 -al 结尾，羰基位于碳链末端，例如乙醛 CH₃CHO。酮的英文名以 -one 结尾，羰基位于碳链内部，例如丙酮 CH₃COCH₃。羰基碳在碳链中总是给予尽可能小的编号。
Carbonyl compounds have permanent dipole–dipole forces because of the polar C=O bond. Therefore their boiling points are higher than those of similar-sized alkanes, but lower than those of corresponding alcohols, because alcohols can form intermolecular hydrogen bonds while simple aldehydes and ketones cannot. Short-chain carbonyls are soluble in water because they can form hydrogen bonds with water molecules.
羰基化合物由于极性的 C=O 键而具有永久偶极–偶极作用力。因此它们的沸点高于分子量相近的烷烃，但低于对应醇，因为醇能形成分子间氢键，而简单的醛和酮不能。短链羰基化合物可溶于水，因为它们能与水分子形成氢键。
3. Nucleophilic Addition with Hydrogen Cyanide | 与氢氰酸的亲核加成
Aldehydes and ketones undergo nucleophilic addition with hydrogen cyanide, HCN, to form hydroxynitriles. The cyanide ion, CN⁻, attacks the δ+ carbonyl carbon, and the C=O π bond breaks to give a negatively charged intermediate. This intermediate then accepts a proton from HCN or acid to form the product.
醛和酮与氢氰酸 HCN 发生亲核加成，生成羟基腈。氰根离子 CN⁻ 进攻 δ+ 的羰基碳，C=O 的 π 键断裂，形成带负电的中间体。该中间体随后从 HCN 或酸中接受质子生成产物。
CH₃CHO + HCN → CH₃CH(OH)CN
The reaction increases the length of the carbon chain by one carbon atom, so it is useful in organic synthesis. The resulting nitrile group can be hydrolysed to a carboxylic acid or reduced to an amine, allowing further transformations. In the laboratory, HCN is often generated in situ from sodium cyanide and dilute sulfuric acid because hydrogen cyanide is extremely toxic.
该反应使碳链增加一个碳原子，因此在有机合成中很有用。生成的腈基可以水解为羧酸或还原为胺，从而进行进一步转化。实验室中常利用氰化钠和稀硫酸现场生成 HCN，因为氢氰酸有剧毒。
4. Reduction and Oxidation of Carbonyls | 羰基化合物的还原与氧化
Both aldehydes and ketones can be reduced to alcohols by strong reducing agents such as lithium aluminium hydride, LiAlH₄, in dry ether, or sodium borohydride, NaBH₄, in aqueous solution. Aldehydes produce primary alcohols, while ketones produce secondary alcohols. In equations, the reducing agent is often written as [H].
醛和酮都能被强还原剂还原为醇，如在干燥乙醚中的氢化铝锂 LiAlH₄，或在水溶液中的硼氢化钠 NaBH₄。醛生成伯醇，酮生成仲醇。在方程式中，还原剂通常写作 [H]。
RCHO + 2[H] → RCH₂OH
R₂CO + 2[H] → R₂CHOH
Aldehydes are easily oxidised to carboxylic acids, but ketones resist oxidation under normal conditions. Acidified potassium dichromate(VI), K₂Cr₂O₇, is a common oxidising agent. The orange solution turns green as Cr₂O₇²⁻ is reduced to Cr³⁺ when an aldehyde is oxidised. This difference is the basis of simple test-tube methods for distinguishing aldehydes from ketones.
醛容易被氧化为羧酸，而酮在通常条件下不易被氧化。酸化重铬酸钾 K₂Cr₂O₇ 是常用氧化剂。当醛被氧化时，橙色溶液因 Cr₂O₇²⁻ 还原为 Cr³⁺ 而变绿。这一差异是试管实验中区分醛和酮的基础。
5. Distinguishing Aldehydes and Ketones | 鉴别醛与酮
Three common reagents are used in the Edexcel syllabus to distinguish aldehydes from ketones: Tollens’ reagent, Fehling’s solution and acidified potassium dichromate(VI). All three oxidise aldehydes but leave ketones unchanged because ketones lack an H atom on the carbonyl carbon.
Edexcel 大纲中常用三种试剂区分醛和酮：Tollens 试剂、Fehling 溶液和酸化重铬酸钾(VI)。三者都能氧化醛，但不能氧化酮，因为酮的羰基碳上没有氢原子。
Tollens’ reagent contains the diamminesilver(I) ion, [Ag(NH₃)₂]⁺. With an aldehyde it produces a silver mirror on the inside of the test tube. Fehling’s solution contains Cu²⁺ in an alkaline complex; with an aldehyde it forms a brick-red precipitate of copper(I) oxide, Cu₂O. Both tests give no visible change with ketones.
Tollens 试剂含有二氨合银(I)离子 [Ag(NH₃)₂]⁺。与醛反应时会在试管内壁生成银镜。Fehling 溶液含有碱性络合物中的 Cu²⁺；与醛反应生成砖红色的氧化亚铜 Cu₂O 沉淀。这两种测试对酮均无可见变化。
| Reagent | Aldehyde | Ketone |
|---|---|---|
| Tollens’ reagent | Silver mirror | No reaction |
| Fehling’s solution | Brick-red precipitate | No reaction |
| Acidified K₂Cr₂O₇ | Orange to green | No reaction |
2,4-Dinitrophenylhydrazine (2,4-DNPH) is also used as a general test for carbonyl compounds. Both aldehydes and ketones give an orange or yellow precipitate with 2,4-DNPH, so it shows the presence of a carbonyl group but does not distinguish between the two.
2,4-二硝基苯肼 (2,4-DNPH) 也可用作羰基化合物的一般检验。醛和酮都能与 2,4-DNPH 生成橙色或黄色沉淀，因此它能证明羰基的存在，但不能区分醛和酮。
6. Carboxylic Acids: Structure and Acidity | 羧酸：结构与酸性
Carboxylic acids contain the carboxyl group, -COOH. They are weak acids because they only partially dissociate in water. The acidic hydrogen is on the hydroxyl group of the carboxyl group, and the resulting carboxylate ion, RCOO⁻, is stabilised by delocalisation of the negative charge over the two oxygen atoms.
羧酸含有羧基 -COOH。它们是弱酸，因为在水溶液中只能部分解离。酸性氢位于羧基的羟基上，生成的羧酸根离子 RCOO⁻ 因负电荷离域到两个氧原子上而更加稳定。
The stronger the acid, the greater the dissociation, so carboxylic acids have a higher Ka and a lower pKa. Electron-withdrawing groups on the R group increase acid strength by stabilising the negative charge on the carboxylate ion. Electron-donating groups decrease acid strength.
酸性越强，解离程度越大，羧酸的 Ka 越大，pKa 越小。R 基上的吸电子基通过稳定羧酸根离子的负电荷而增强酸性。给电子基则降低酸性。
Carboxylic acids react with metals, bases and carbonates to form salts. For example, ethanoic acid reacts with sodium carbonate to give sodium ethanoate, carbon dioxide and water. This effervescence with carbonates is a simple test for carboxylic acids.
羧酸能与金属、碱和碳酸盐反应生成盐。例如，乙酸与碳酸钠反应生成乙酸钠、二氧化碳和水。与碳酸盐产生气泡是检验羧酸的简单方法。
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O
7. Esterification and Ester Hydrolysis | 酯化与酯水解
Carboxylic acids react with alcohols in the presence of a strong acid catalyst, usually concentrated sulfuric acid, to form esters and water. This is called esterification and is a reversible condensation reaction. The reaction is slow at room temperature, so it is heated under reflux.
羧酸与醇在强酸催化剂（通常为浓硫酸）存在下反应生成酯和水。这称为酯化反应，是一个可逆的缩合反应。该反应在室温下缓慢，因此需要在回流条件下加热。
RCOOH + R’OH ⇌ RCOOR’ + H₂O
Esters have the functional group -COO-. They are commonly used as solvents, plasticisers, flavourings and fragrances. Ester hydrolysis can be carried out under acidic or alkaline conditions. Acid hydrolysis is the reverse of esterification, while alkaline hydrolysis using aqueous sodium hydroxide goes to completion because the carboxylic acid formed is neutralised to a carboxylate salt.
酯的官能团是 -COO-。它们常用作溶剂、增塑剂、香料和香精。酯的水解可在酸性或碱性条件下进行。酸水解是酯化的逆反应，而使用氢氧化钠水溶液的碱水解可以彻底完成，因为生成的羧酸被中和为羧酸盐。
RCOOR’ + H₂O ⇌ RCOOH + R’OH
8. Acyl Chlorides: Nucleophilic Addition–Elimination | 酰氯：亲核加成–消除
Acyl chlorides have the functional group -COCl. They are more reactive than carboxylic acids and esters because the chlorine atom withdraws electron density strongly, making the carbonyl carbon more positive. They react readily with nucleophiles by a nucleophilic addition–elimination mechanism.
酰氯的官能团是 -COCl。它们比羧酸和酯更活泼，因为氯原子强烈吸电子，使羰基碳更正。它们通过亲核加成–消除机理与亲核试剂迅速反应。
In the first step the nucleophile attacks the carbonyl carbon, forming a tetrahedral intermediate. In the second step the C–Cl bond breaks and the chloride ion is eliminated. Common nucleophiles include water, alcohols, ammonia and primary amines. The products are carboxylic acids, esters, amides and N-substituted amides respectively.
第一步，亲核试剂进攻羰基碳，形成四面体中间体。第二步，C–Cl 键断裂，氯离子被消除。常见的亲核试剂有水、醇、氨和伯胺，产物分别为羧酸、酯、酰胺和 N-取代酰胺。
RCOCl + H₂O → RCOOH + HCl
RCOCl + R’OH → RCOOR’ + HCl
RCOCl + 2NH₃ → RCONH₂ + NH₄Cl
Acyl chlorides are prepared from carboxylic acids using reagents such as phosphorus(V) chloride, PCl₅, phosphorus(III) chloride, PCl₃, or thionyl chloride, SOCl₂. Thionyl chloride is often preferred because the other products are gases that escape from the mixture.
酰氯可由羧酸与五氯化磷 PCl₅、三氯化磷 PCl₃ 或亚硫酰氯 SOCl₂ 等试剂反应制得。通常优先使用亚硫酰氯，因为其他产物是气体，可以从混合物中逸出。
9. Chirality and Optical Isomerism | 手性与光学异构
Optical isomerism occurs when a molecule contains a chiral carbon atom, which is a carbon atom bonded to four different groups. The two isomers are non-superimposable mirror images of each other, called enantiomers. They differ only in the direction in which they rotate plane-polarised light.
当分子含有手性碳原子，即与四个不同基团相连的碳原子时，会产生光学异构。两种异构体互为不可重叠的镜像，称为对映异构体。它们仅在使平面偏振光旋转的方向上有所不同。
The reaction of an aldehyde or an unsymmetrical ketone with HCN can produce a racemic mixture because the nucleophile attacks the planar carbonyl group from above and below with equal probability. This leads to equal amounts of the two enantiomers, which has no overall optical activity.
醛或不饱和酮与 HCN 反应可生成外消旋混合物，因为亲核试剂从平面羰基的上方和下方进攻的概率相等。这会生成等量的两种对映异构体，整体没有光学活性。
In the Edexcel exam you must be able to identify chiral centres, draw three-dimensional representations and explain why a racemic mixture is formed. You should not confuse optical isomerism with E/Z isomerism, which arises from restricted rotation around a double bond.
在 Edexcel 考试中，你必须能够识别手性中心，绘制三维结构图，并解释为何会生成外消旋混合物。不要将光学异构与 E/Z 异构混淆，后者由双键的限制旋转引起。
10. Condensation Polymers: Polyesters and Polyamides | 缩合聚合物：聚酯与聚酰胺
Condensation polymers are formed when monomers join together with the elimination of a small molecule such as water or HCl. Two important classes are polyesters and polyamides. They are made from bifunctional monomers, meaning each monomer has two reactive groups.
缩合聚合物是由单体连接并脱去水或 HCl 等小分子而形成的。两类重要的缩合聚合物是聚酯和聚酰胺。它们由双官能团单体制成，即每个单体具有两个反应基团。
A polyester is formed from a diol and a dicarboxylic acid or a diacyl chloride. For example, ethane-1,2-diol and benzene-1,4-dicarboxylic acid produce the polyester commonly known as Terylene. A polyamide is formed from a diamine and a dicarboxylic acid or diacyl chloride. Nylon-6,6 is made from hexane-1,6-diamine and hexane-1,6-dioic acid.
聚酯由二元醇与二元羧酸或二酰氯生成。例如，乙二醇与对苯二甲酸生成俗称涤纶的聚酯。聚酰胺由二元胺与二元羧酸或二酰氯生成。尼龙-6,6 由己二胺和己二酸制成。
nHO(CH₂)₂OH + nHOOC-C₆H₄-COOH → [O(CH₂)₂OOC-C₆H₄-CO]n + 2nH₂O
Condensation polymers can be hydrolysed back into their monomers by heating with acid or base. Polyesters are more easily hydrolysed than polyamides because the ester link is more reactive than the amide link. This has important implications for recycling and environmental degradation.
缩合聚合物可在酸或碱加热条件下水解回单体。聚酯比聚酰胺更容易水解，因为酯键比酰胺键更活泼。这对回收和环境降解有重要意义。
11. Summary and Exam Tips | 总结与考试建议
Topic 17 connects many organic reactions through the carbonyl group. Remember that aldehydes can be oxidised but ketones cannot, both undergo nucleophilic addition, carboxylic acids are weak acids, esters are formed reversibly, acyl chlorides react by addition–elimination, and bifunctional monomers form condensation polymers.
第17章通过羰基把许多有机反应联系在一起。记住：醛能被氧化而酮不能；两者都能发生亲核加成；羧酸是弱酸；酯的可逆生成；酰氯通过加成–消除反应；双官能团单体形成缩合聚合物。
When writing mechanisms, always show the nucleophile attacking the δ+ carbonyl carbon and the breaking of the π bond. For acyl chlorides, include the elimination of the chloride ion. When answering isomerism questions, draw the tetrahedral arrangement clearly and label the chiral centre.
书写机理时，一定要画出亲核试剂进攻 δ+ 羰基碳和 π 键断裂。对于酰氯，要包含氯离子的消除。回答异构体问题时，要清晰地画出四面体排列并标记手性中心。
- Use balanced equations with correct molecular formulas and conditions.
- Link physical properties to intermolecular forces, not just memorise trends.
- Practise distinguishing tests in tables to avoid confusion in exams.
- Remember that condensation polymerisation involves small-molecule elimination.
- Check for chiral centres whenever four different groups are attached to one carbon.
使用正确的分子式和条件书写配平的方程式。将物理性质与分子间作用力联系起来，而不仅仅是记忆规律。练习用表格整理鉴别试验，避免考试时混淆。记住缩合聚合涉及小分子消除。当一个碳上连有四个不同基团时，检查手性中心。
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导