📚 A-Level Organic Chemistry Reaction Summary | A-Level有机化学反应总结
Organic chemistry at A-Level is built around a core set of reaction types, each with characteristic mechanisms, reagents, and conditions. Understanding these reaction summaries is crucial for predicting products, designing synthesis pathways, and answering mechanism questions. This article provides a concise yet comprehensive overview of the key organic reactions you need to master.
A-Level有机化学围绕着一组核心反应类型展开，每种反应都具有特定的机理、试剂与条件。掌握这些反应总结对于预测产物、设计合成路线以及解答机理题至关重要。本文将简明而全面地概述你需掌握的关键有机反应。
1. Free Radical Substitution of Alkanes | 烷烃的自由基取代
Alkanes react with halogens (typically Cl₂ or Br₂) in the presence of ultraviolet (UV) light through a free radical chain mechanism. This reaction produces a mixture of halogenoalkanes and hydrogen halide.
烷烃在紫外光照射下与卤素（通常为Cl₂或Br₂）发生自由基链式反应，生成卤代烷和卤化氢的混合物。
CH₄ + Cl₂ —UV→ CH₃Cl + HCl
The mechanism involves three stages: initiation (homolytic fission of the halogen bond to form radicals), propagation (radicals react with molecules to produce new radicals and products), and termination (two radicals combine).
机理分为三个阶段：引发（卤素键均裂生成自由基）、增长（自由基与分子反应产生新的自由基和产物）和终止（两个自由基结合）。
Further substitution can occur because the product chloroalkane can undergo additional radical reactions, leading to polychlorinated products. Controlling the ratio of reactants helps favour monosubstitution.
由于产物氯代烷可继续参与自由基反应，会发生进一步取代，生成多氯代产物。控制反应物比例有助于促进单取代。
2. Electrophilic Addition of Alkenes | 烯烃的亲电加成
Alkenes contain a carbon–carbon double bond that acts as an electron-rich centre, attacking electrophilic species. Electrophilic addition is the characteristic reaction of alkenes, occurring with hydrogen (H₂ with Ni catalyst), halogens (X₂), hydrogen halides (HX), and even steam (H₂O with H₃PO₄ catalyst).
烯烃含有碳碳双键，作为富电子中心进攻亲电物种。亲电加成是烯烃的特征反应，可与氢气（H₂，Ni催化）、卤素（X₂）、卤化氢（HX）甚至水蒸气（H₂O，H₃PO₄催化）发生反应。
CH₃CH=CH₂ + HBr → CH₃CHBrCH₃ (major product)
When adding a hydrogen halide to an unsymmetrical alkene, Markovnikov’s rule applies: the hydrogen atom attaches to the carbon with the greater number of hydrogen atoms already bonded. This is because the more stable carbocation intermediate forms preferentially.
当卤化氢与不对称烯烃加成时，遵循马氏规则：氢原子加在原来连有较多氢原子的碳上。这是因为更稳定的碳正离子中间体优先形成。
Bromine water (orange to colourless) is a test for unsaturation. The addition of Br₂ proceeds rapidly at room temperature, decolourising the bromine solution without UV requirement.
溴水（橙色变为无色）是检验不饱和键的试剂。Br₂在室温下迅速加成，无需紫外光即可使溴溶液褪色。
3. Nucleophilic Substitution of Halogenoalkanes | 卤代烷的亲核取代
Halogenoalkanes contain a polar carbon–halogen bond that leaves the carbon atom electron-deficient and susceptible to attack by nucleophiles. Common nucleophiles include OH⁻, CN⁻, and NH₃. The reaction can proceed via either an SN1 or SN2 mechanism depending on the structure of the halogenoalkane.
卤代烷含有极性的碳–卤键，使得碳原子缺电子，易受亲核试剂进攻。常见亲核试剂包括OH⁻、CN⁻和NH₃。反应可按SN1或SN2机理进行，取决于卤代烷的结构。
CH₃CH₂Br + NaOH (aq, warm) → CH₃CH₂OH + NaBr
Tertiary halogenoalkanes favour SN1 via a planar carbocation intermediate, while primary halogenoalkanes proceed via SN2 with inversion of configuration. The rate of SN2 depends on both the halogenoalkane and the nucleophile concentration, whereas SN1 rate depends only on the halogenoalkane.
叔卤代烷倾向于通过平面碳正离子中间体的SN1机理，伯卤代烷则经由构型翻转的SN2机理。SN2速率取决于卤代烷和亲核试剂浓度，而SN1速率只取决于卤代烷浓度。
Heating a halogenoalkane with aqueous potassium hydroxide yields an alcohol; with ethanolic potassium cyanide, a nitrile (extending the carbon chain); and with excess ethanolic ammonia, an amine is produced.
卤代烷与氢氧化钾水溶液加热得醇；与氰化钾乙醇溶液加热得腈（增长碳链）；与过量氨的乙醇溶液加热则生成胺。
4. Elimination Reactions of Halogenoalkanes | 卤代烷的消去反应
When a halogenoalkane is heated with potassium hydroxide dissolved in ethanol (rather than water), elimination competes with substitution, producing an alkene, water, and a halide salt. This is an example of a β-elimination.
当卤代烷与溶于乙醇（而非水）的氢氧化钾加热时，消去反应与取代竞争，生成烯烃、水和卤化物盐。这是β-消去的实例。
CH₃CHBrCH₃ + KOH (ethanolic, heat) → CH₂=CHCH₃ + KBr + H₂O
The hydroxide ion acts as a base, abstracting a β-hydrogen atom. The reaction proceeds via an E2 mechanism for primary substrates and can follow E1 for tertiary ones. Hot ethanolic conditions favour elimination over nucleophilic substitution.
氢氧根离子作为碱，夺取β-氢原子。对于伯卤代烷按E2机理进行，叔卤代烷可按E1机理。热的乙醇条件有利于消去而非亲核取代。
When a mixture of substitution and elimination is possible, the proportion of alkene increases with the use of a strong, bulky base and higher temperature. Saytzeff’s rule often applies: the more substituted alkene is the major product.
当取代和消去均可发生时，使用强而体积大的碱以及升高温度会增加烯烃比例。通常遵循扎伊采夫规则：取代更多的烯烃为主要产物。
5. Oxidation of Alcohols | 醇的氧化
Alcohols can be oxidised using acidified potassium dichromate(VI) (K₂Cr₂O₇/H₂SO₄). The outcome depends on the class of alcohol and the reaction conditions. The colour change from orange to green indicates successful oxidation.
醇可用酸化的重铬酸钾(VI) (K₂Cr₂O₇/H₂SO₄)氧化。结果取决于醇的类型和反应条件。颜色由橙变绿表明氧化成功。
Primary alcohols are first oxidised to aldehydes, which can be isolated by distillation; further oxidation yields carboxylic acids when the mixture is heated under reflux.
伯醇首先被氧化成醛，可通过蒸馏分离；进一步加热回流氧化则生成羧酸。
CH₃CH₂OH + [O] → CH₃CHO + H₂O; then CH₃CHO + [O] → CH₃COOH
Secondary alcohols are oxidised to ketones. No further oxidation occurs under standard conditions because breaking a C–C bond would be required. Tertiary alcohols are not oxidised by acidified dichromate.
仲醇被氧化成酮。在标准条件下不会再被氧化，因为这将需要断裂C–C键。叔醇不能被酸化的重铬酸盐氧化。
A specific reagent, such as pyridinium chlorochromate (PCC), can be used for controlled oxidation of primary alcohols to aldehydes without over-oxidation to the acid.
特定试剂如氯铬酸吡啶(PCC)可用于伯醇的控制氧化得到醛，避免过度氧化为酸。
6. Reactions of Carbonyl Compounds | 羰基化合物的反应
Aldehydes and ketones undergo nucleophilic addition due to the polarised C=O bond. Both react with hydrogen cyanide (HCN) to form hydroxynitriles (cyanohydrins), extending the carbon chain.
由于极化的C=O键，醛和酮发生亲核加成。两者均与氰化氢(HCN)反应生成羟基腈（氰醇），增长碳链。
CH₃COCH₃ + HCN → CH₃C(OH)(CN)CH₃
Sodium tetrahydridoborate(III) (NaBH₄) reduces aldehydes to primary alcohols and ketones to secondary alcohols in aqueous or alcoholic solution. Lithium aluminium hydride (LiAlH₄) is a stronger reducing agent used in dry ether.
四氢硼酸钠(NaBH₄)在水或醇溶液中可将醛还原为伯醇，酮还原为仲醇。氢化铝锂(LiAlH₄)是更强的还原剂，用于干燥乙醚中。
Brady’s reagent (2,4-dinitrophenylhydrazine) gives a yellow/orange precipitate with both aldehydes and ketones, confirming the carbonyl group. Distinguishing between them uses Tollens’ reagent (silver mirror with aldehydes) or Fehling’s solution (red precipitate with aldehydes only).
Brady试剂（2,4-二硝基苯肼）与醛和酮均产生黄/橙色沉淀，确认羰基。区分二者可使用Tollens试剂（醛有银镜）或Fehling溶液（只有脂肪醛产生红色沉淀）。
7. Reactions of Carboxylic Acids | 羧酸的反应
Carboxylic acids are weak acids, reacting with metals, bases, and carbonates to form salts and water (or CO₂). Their most important synthetic reaction is esterification, where an acid reacts with an alcohol in the presence of a strong acid catalyst.
羧酸是弱酸，能与金属、碱和碳酸盐反应生成盐和水（或CO₂）。其最重要的合成反应是酯化反应，在强酸催化剂存在下与醇反应。
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O (H⁺ catalyst, reflux)
Esterification is a reversible condensation reaction. The equilibrium can be shifted to the right by using an excess of one reactant or by removing water as it forms. Carboxylic acids can also be reduced to primary alcohols by LiAlH₄.
酯化是可逆的缩合反应。通过使用过量一种反应物或移去生成的水，可使平衡向右移动。羧酸也可被LiAlH₄还原为伯醇。
Carboxylic acids react with phosphorus(V) chloride (PCl₅) to form acyl chlorides, but more commonly thionyl chloride (SOCl₂) is used. The hydroxyl group is replaced by a chlorine atom under mild heating.
羧酸与五氯化磷(PCl₅)反应生成酰氯，但更常用氯化亚砜(SOCl₂)。在温和加热下羟基被氯原子取代。
8. Reactions of Acyl Chlorides and Acid Anhydrides | 酰氯与酸酐的反应
Acyl chlorides (RCOCl) and acid anhydrides ((RCO)₂O) are highly reactive carboxylic acid derivatives. They undergo nucleophilic addition–elimination (also called acylation) with water, alcohols, ammonia, and amines.
酰氯(RCOCl)和酸酐((RCO)₂O)是高活性的羧酸衍生物，可与水、醇、氨和胺发生亲核加成–消除（也称酰化反应）。
CH₃COCl + C₂H₅OH → CH₃COOC₂H₅ + HCl
With alcohols they produce esters, with ammonia they give amides, and with primary amines they produce N-substituted amides. The reactions are vigorous and do not require a catalyst, unlike esterification with carboxylic acid.
与醇反应生成酯，与氨生成酰胺，与伯胺生成N-取代酰胺。这些反应剧烈，无需催化剂，与使用羧酸的酯化不同。
Acid anhydrides react similarly but are often preferred in the laboratory for preparing aspirin because they are safer and less violent than acyl chlorides, producing a carboxylic acid as a by-product instead of HCl.
酸酐反应类似，但在实验室制备阿司匹林时更常用，因为它们比酰氯更安全、反应更温和，副产物是羧酸而非HCl。
9. Electrophilic Substitution of Aromatic Compounds | 芳烃的亲电取代
Benzene and its derivatives undergo electrophilic substitution rather than addition, preserving the stable delocalised π-electron system. Key reactions include nitration, halogenation, and Friedel–Crafts alkylation or acylation.
苯及其衍生物发生亲电取代而非加成，从而保持稳定的离域π电子体系。关键反应包括硝化、卤化和Friedel–Crafts烷基化或酰化。
C₆H₆ + HNO₃ —(H₂SO₄ catalyst, 50°C)→ C₆H₅NO₂ + H₂O
Nitration uses a mixture of concentrated nitric and sulfuric acids. The electrophile is the nitronium ion (NO₂⁺), generated by the reaction of HNO₃ with H₂SO₄. Halogenation requires a halogen carrier such as AlCl₃ or FeBr₃ to generate the electrophile X⁺.
硝化使用浓硝酸和浓硫酸的混合物。亲电试剂是硝酰正离子(NO₂⁺)，由HNO₃与H₂SO₄反应产生。卤化需要卤素载体如AlCl₃或FeBr₃以产生亲电试剂X⁺。
Friedel–Crafts alkylation introduces a carbon chain using a haloalkane and AlCl₃, forming an alkylbenzene. Acylation uses an acyl chloride to produce a ketone. Both generate a carbocation as the attacking electrophile.
Friedel–Crafts烷基化使用卤代烷和AlCl₃引入碳链，生成烷基苯。酰化使用酰氯生成酮。两者均产生碳正离子作为进攻的亲电试剂。
10. Addition Polymerisation | 加成聚合
Alkenes can undergo addition polymerisation, where the double bonds open up and monomers join together to form a long saturated chain. This process is initiated by radicals, and the product is a polymer such as poly(ethene) or poly(propene).
烯烃可发生加成聚合，双键打开，单体相互连接形成长饱和链。该过程由自由基引发，产物为聚乙烯、聚丙烯等聚合物。
n CH₂=CH₂ → —[CH₂–CH₂]ₙ—
The repeating unit of an addition polymer is derived directly from the monomer without loss of any small molecule. The polymer name is the prefix ‘poly’ followed by parentheses around the monomer name: poly(ethene).
加聚物的重复单元直接源自单体，没有小分子脱除。聚合物命名是在单体名称外加上括号并冠以“聚”字，如聚(乙烯)。
Addition polymers are typically non-biodegradable and are used extensively in plastics and packaging. The properties can be tailored by controlling chain length, branching, and crystallinity.
加聚物通常不可生物降解，广泛应用于塑料和包装。可通过控制链长、支化和结晶度来调控性能。
11. Condensation Polymerisation | 缩合聚合
Condensation polymers are formed from monomers bearing two functional groups, with the elimination of a small molecule such as water or HCl during polymerisation. Two main classes are polyesters and polyamides.
缩聚物由带有两个官能团的单体形成，聚合过程中脱除小分子如水或HCl。主要分为聚酯和聚酰胺两类。
n HO–(CH₂)₂–OH + n HOOC–(CH₂)₄–COOH → —[O–(CH₂)₂–O–CO–(CH₂)₄–CO]ₙ— + (2n-1) H₂O
Polyesters are produced from a diol and a dicarboxylic acid (or a diacyl chloride). Terylene is a well-known example made from ethane-1,2-diol and benzene-1,4-dicarboxylic acid.
聚酯由二醇与二羧酸（或二酰氯）制得。涤纶（Terylene）是著名的例子，由乙二醇和对苯二甲酸制成。
Polyamides (nylons) form from a diamine and a dicarboxylic acid or from amino acids. The amide linkage –CONH– is formed. Kevlar is a polyamide with exceptional strength owing to strong intermolecular hydrogen bonds.
聚酰胺（尼龙）由二胺和二羧酸或氨基酸形成，生成酰胺键–CONH–。凯夫拉（Kevlar）是一种聚酰胺，因其强大的分子间氢键而具有卓越的强度。
12. Key Oxidising and Reducing Agents in Organic Synthesis | 有机合成中的关键氧化剂与还原剂
Mastering the common reagents for oxidation and reduction is essential for planning synthesis pathways. The choice of reagent depends on the functional group to be transformed and the required selectivity.
掌握常见的氧化与还原试剂对于规划合成路线至关重要。试剂的选择取决于待转化的官能团和所需的选择性。
| Reagent | Action | Typical Transformation |
|---|---|---|
| K₂Cr₂O₇/H⁺ | Oxidising | 1° alcohol → aldehyde → carboxylic acid; 2° alcohol → ketone |
| NaBH₄ | Reducing | Aldehydes → 1° alcohols; Ketones → 2° alcohols |
| LiAlH₄ in dry ether | Strong Reducing | Carboxylic acids, esters → 1° alcohols; Amides → amines |
| H₂ / Ni catalyst | Hydrogenation | Alkenes → alkanes; Nitriles → amines |
In addition, Tollens’ reagent (ammoniacal silver nitrate) is a mild oxidising agent used specifically to test for aldehydes, while potassium manganate(VII) is a strong oxidant capable of cleaving double bonds under vigorous conditions.
此外，Tollens试剂（银氨溶液）是专门用于检验醛的温和氧化剂，而高锰酸钾是一种强氧化剂，在剧烈条件下可断裂双键。
When designing a synthetic route, consider the compatibility of reagents with other functional groups present and use protective groups if necessary. The reactions summarised above form an interconnected web that is at the heart of A-Level organic chemistry.
在设计合成路线时，需考虑试剂与分子中其他官能团的相容性，必要时使用保护基。上述总结的反应构成了一个相互关联的网络，这正是A-Level有机化学的核心。
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