Mastering Organic Chemistry | 掌握有机化学

📚 Mastering Organic Chemistry | 掌握有机化学

Organic chemistry is the study of carbon-based compounds, which form the backbone of life and modern industry. For AQA A-Level Chemistry, this topic spans both Year 1 and Year 2 content and is tested across all three papers. A systematic understanding of functional groups, reaction mechanisms and analytical techniques is essential for success.

有机化学是研究含碳化合物的科学，含碳化合物是生命与现代工业的基础。对于 AQA A-Level 化学而言，本专题横跨第一年与第二年的教学内容，并在三张试卷中均有考查。系统地理解官能团、反应机理与分析技术是取得高分的关键。

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1. Nomenclature & Isomerism | 命名与同分异构

The IUPAC naming system is fundamental: identify the longest carbon chain containing the principal functional group, number it to give the lowest locants to substituents, and list substituents alphabetically. Functional group priority determines the suffix, e.g., -ol for alcohols, -al for aldehydes, and -oic acid for carboxylic acids.

IUPAC 命名系统是基础：找出包含主要官能团的最长碳链，对其进行编号使取代基的位次数字最小，并按字母顺序排列取代基。官能团的优先级决定后缀，例如：醇用 -ol，醛用 -al，羧酸用 -oic acid。

Structural isomerism arises when compounds share the same molecular formula but differ in atom connectivity. Three types exist: chain isomerism (varying branching), position isomerism (functional group location) and functional group isomerism (different functional groups, e.g., propanal and propanone).

结构同分异构发生于化合物具有相同分子式但原子连接方式不同的情形。共有三种类型：碳链异构（支链不同）、位置异构（官能团位置不同）和官能团异构（官能团种类不同，例如丙醛与丙酮）。

Stereoisomerism concerns compounds with identical connectivity but different spatial arrangements. E/Z isomerism occurs around double bonds when each carbon of the C=C bears two different substituents; E has the priority groups on opposite sides, Z on the same side. Optical isomerism involves non-superimposable mirror images called enantiomers; a carbon atom bonded to four different groups creates a chiral centre.

立体异构涉及连接方式相同但空间排列不同的化合物。E/Z 异构发生在双键两端各碳原子连接两个不同基团时；E 构型中优先基团位于对侧，Z 构型中位于同侧。光学异构涉及不可重叠的镜像体，称为对映体；碳原子连接四个不同基团时形成手性中心。

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2. Alkanes & Free Radical Substitution | 烷烃与自由基取代

Alkanes are saturated hydrocarbons containing only C-C and C-H sigma bonds. They are relatively unreactive due to strong non-polar bonds, but undergo combustion and free radical substitution under UV light.

烷烃是仅含 C-C 和 C-H σ 键的饱和烃。由于键为非极性且键能较强，烷烃相对不活泼，但在紫外光照射下可发生燃烧和自由基取代反应。

The free radical substitution of methane with chlorine proceeds through three stages:

甲烷与氯气的自由基取代反应分三个阶段进行：

Initiation: Cl₂ → 2Cl• (UV light, homolytic fission of the Cl-Cl bond)

起始：Cl₂ → 2Cl•（紫外光，Cl-Cl 键发生均裂）

Propagation: Cl• + CH₄ → HCl + •CH₃, then •CH₃ + Cl₂ → CH₃Cl + Cl• (the Cl• radical is regenerated)

链增长：Cl• + CH₄ → HCl + •CH₃，随后 •CH₃ + Cl₂ → CH₃Cl + Cl•（Cl• 自由基再生）

Termination: radical combination steps, e.g., •CH₃ + Cl• → CH₃Cl, or Cl• + Cl• → Cl₂

链终止：自由基结合步骤，例如 •CH₃ + Cl• → CH₃Cl，或 Cl• + Cl• → Cl₂

A key limitation of this reaction is that further substitution produces a mixture of products (CH₂Cl₂, CHCl₃, CCl₄), making it poor for synthesis.

该反应的关键局限在于进一步取代会产生混合物（CH₂Cl₂、CHCl₃、CCl₄），因此不适宜用于合成制备。

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3. Alkenes & Electrophilic Addition | 烯烃与亲电加成

Alkenes contain a C=C double bond composed of one sigma bond and one pi bond. The pi bond is an area of high electron density, making alkenes nucleophilic and reactive toward electrophiles.

烯烃含有 C=C 双键，由一个 σ 键和一个 π 键组成。π 键是电子密度高的区域，使烯烃具有亲核性，容易与亲电试剂发生反应。

The general mechanism is electrophilic addition. For example, ethene reacts with bromine: the Br₂ molecule becomes polarised as it approaches the electron-rich double bond; the δ⁺ bromine atom acts as an electrophile, forming a bromonium ion intermediate; the Br⁻ then attacks to yield 1,2-dibromoethane.

一般机理为亲电加成。例如，乙烯与溴反应：Br₂ 分子接近电子富集的双键时发生极化；带 δ⁺ 的溴原子作为亲电试剂进攻，形成溴鎓离子中间体；随后 Br⁻ 进攻生成 1,2-二溴乙烷。

With unsymmetrical alkenes, Markovnikov’s rule applies: the hydrogen atom adds to the carbon of the double bond that already has more hydrogen atoms. For example, propene + HBr gives 2-bromopropane as the major product, because the secondary carbocation intermediate is more stable than the primary one.

对于不对称烯烃，马尔科夫尼科夫规则适用：氢原子加到双键碳中原本含氢较多的那个碳上。例如，丙烯与 HBr 加成的主要产物是 2-溴丙烷，因为仲碳正离子中间体比伯碳正离子更稳定。

Key addition reactions include: hydrogenation (H₂/Ni) to form alkanes, halogenation (Br₂) and the test with bromine water which decolorises from orange to colourless, hydration (H₂O/H₃PO₄) to form alcohols, and addition of hydrogen halides (HX).

重要的加成反应包括：加氢（H₂/Ni）生成烷烃、加卤素（Br₂）以及溴水褪色测试（从橙色变为无色）、水合（H₂O/H₃PO₄）生成醇，以及加入卤化氢（HX）。

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4. Halogenoalkanes | 卤代烷烃

Halogenoalkanes contain a polar C-X bond (X = F, Cl, Br, I) because the halogen is more electronegative than carbon. The carbon atom carries a partial positive charge and is susceptible to attack by nucleophiles.

卤代烷烃含有极性的 C-X 键（X = F、Cl、Br、I），因为卤素的电负性大于碳。碳原子带有部分正电荷，容易受到亲核试剂的进攻。

Nucleophilic substitution occurs with aqueous hydroxide ions: C₂H₅Br + NaOH(aq) → C₂H₅OH + NaBr. The mechanism may be SN2 (one step, backside attack, favoured by primary halogenoalkanes) or SN1 (two steps, carbocation intermediate, favoured by tertiary halogenoalkanes).

亲核取代反应在水相氢氧根离子存在下发生：C₂H₅Br + NaOH(aq) → C₂H₅OH + NaBr。机理可为 SN2（一步完成，背面进攻，伯卤代烷烃优先）或 SN1（两步完成，碳正离子中间体，叔卤代烷烃优先）。

Reactivity trends: tertiary > secondary > primary for SN1, while primary > secondary > tertiary for SN2. The C-I bond is weaker than C-Br or C-Cl, so iodoalkanes react fastest. This is exploited in the hydrolysis test: adding ethanolic silver nitrate and comparing the rate of AgX precipitate formation (AgCl white, AgBr cream, AgI yellow).

反应活性顺序：SN1 中叔卤代烷 > 仲 > 伯，SN2 中伯卤代烷 > 仲 > 叔。C-I 键比 C-Br 或 C-Cl 键弱，因此碘代烷反应最快。这一点被用于水解测试：加入乙醇硝酸银溶液，比较卤化银沉淀生成速率（AgCl 白色、AgBr 淡黄色、AgI 黄色）。

Halogenoalkanes also undergo elimination with hot ethanolic NaOH, producing alkenes: e.g., C₂H₅Br + NaOH(ethanol) → C₂H₄ + NaBr + H₂O.

卤代烷烃还可与热的乙醇 NaOH 发生消除反应生成烯烃：例如 C₂H₅Br + NaOH(乙醇) → C₂H₄ + NaBr + H₂O。

In atmospheric chemistry, CFCs (chlorofluorocarbons) release chlorine radicals under UV light; each Cl• radical can destroy thousands of ozone molecules; ozone depletion is a serious environmental consequence.

在大气化学中，CFC（氯氟烃）在紫外光下释放氯自由基；每个 Cl• 自由基可破坏数千个臭氧分子，臭氧层损耗是严重的环境后果。

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5. Alcohols | 醇

Alcohols contain the hydroxyl (-OH) functional group. They are classified as primary, secondary or tertiary depending on how many carbon atoms are attached to the carbon bearing the -OH group.

醇含有羟基（-OH）官能团。根据连接 -OH 的碳原子上所连碳原子数，醇分为伯醇、仲醇和叔醇。

Oxidation with acidified potassium dichromate (K₂Cr₂O₇/H₂SO₄) gives:

使用酸性重铬酸钾（K₂Cr₂O₇/H₂SO₄）氧化时：

• Primary alcohols → aldehydes (on distillation) → carboxylic acids (with reflux)

• 伯醇 → 醛（蒸馏条件下）→ 羧酸（回流条件下）

• Secondary alcohols → ketones only

• 仲醇 → 酮（不能再进一步氧化）

• Tertiary alcohols are not oxidised under these conditions

• 叔醇在此条件下不发生氧化

The colour change from orange to green indicates a successful oxidation reaction.

溶液颜色从橙色变为绿色表明氧化反应已经发生。

Dehydration of alcohols produces alkenes: pass ethanol vapour over heated aluminium oxide catalyst (Al₂O₃, ~300°C) or heat with concentrated sulfuric acid. For example, ethanol → ethene + H₂O.

醇的脱水反应可生成烯烃：将乙醇蒸气通过加热的氧化铝催化剂（Al₂O₃，约 300°C），或与浓硫酸共热。例如：乙醇 → 乙烯 + H₂O。

Esterification involves reacting an alcohol with a carboxylic acid in the presence of concentrated H₂SO₄ catalyst. The product is an ester with a characteristic fruity smell, e.g., ethanol + ethanoic acid ⇌ ethyl ethanoate + H₂O.

酯化反应是醇与羧酸在浓 H₂SO₄ 催化下进行。产物为具有水果香味的酯，例如：乙醇 + 乙酸 ⇌ 乙酸乙酯 + H₂O。

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6. Aldehydes & Ketones | 醛与酮

Aldehydes have the -CHO group at the end of a chain; ketones have the carbonyl group within the chain (C=O attached to two carbon atoms). Both contain the polar carbonyl group, which undergoes nucleophilic addition.

醛的 -CHO 基团位于碳链末端；酮的羰基位于碳链内部（C=O 连接两个碳原子）。两者都含有极性的羰基，可发生亲核加成反应。

Aldehydes reduce Tollens’ reagent (ammoniacal silver nitrate) producing a silver mirror, and reduce Fehling’s solution producing a brick-red precipitate of Cu₂O. Ketones do not react with either reagent; this provides a reliable distinguishing test.

醛能还原 Tollens 试剂（氨性硝酸银）产生银镜，也能还原 Fehling 溶液产生砖红色 Cu₂O 沉淀。酮与这两种试剂均不反应，这提供了可靠的鉴别方法。

Nucleophilic addition of HCN (with KCN and H⁺) to an aldehyde or ketone gives a hydroxynitrile. The reaction increases the carbon chain length and, when the carbonyl compound is unsymmetrical, creates a new chiral centre, producing a racemic mixture.

HCN（与 KCN 和 H⁺ 配合）对醛或酮进行亲核加成生成羟基腈。该反应延长了碳链，并且当羰基化合物不对称时生成新的手性中心，得到外消旋混合物。

NaBH₄ (sodium borohydride) reduces aldehydes to primary alcohols and ketones to secondary alcohols. For example, propanal → propan-1-ol; propanone → propan-2-ol.

NaBH₄（硼氢化钠）可将醛还原为伯醇，将酮还原为仲醇。例如：丙醛 → 丙-1-醇；丙酮 → 丙-2-醇。

RCHO + 2[H] → RCH₂OH (aldehyde → primary alcohol)

RCHO + 2[H] → RCH₂OH（醛 → 伯醇）

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7. Carboxylic Acids & Derivatives | 羧酸及其衍生物

Carboxylic acids contain the -COOH group and are weak acids: CH₃COOH ⇌ CH₃COO⁻ + H⁺. They react with alkalis, carbonates and reactive metals to form salts, and they undergo esterification with alcohols as described above.

羧酸含有 -COOH 基团，是弱酸：CH₃COOH ⇌ CH₃COO⁻ + H⁺。它们与碱、碳酸盐和活泼金属反应生成盐，并可与醇发生酯化反应（如前所述）。

Acyl chlorides (e.g., ethanoyl chloride, CH₃COCl) are much more reactive derivatives. They react vigorously with water, alcohols, ammonia and amines to form carboxylic acids, esters, primary amides and N-substituted amides respectively. HCl gas is released in each case.

酰氯（例如乙酰氯，CH₃COCl）是反应活性更高的衍生物。它们分别与水、醇、氨和胺剧烈反应生成羧酸、酯、伯酰胺和 N-取代酰胺，每个反应都释放 HCl 气体。

Acid anhydrides (e.g., ethanoic anhydride) undergo similar reactions but are safer and less corrosive; ethanoic anhydride is often used in the industrial preparation of aspirin from salicylic acid.

酸酐（例如乙酸酐）发生类似反应但更安全、腐蚀性更低；乙酸酐常用于工业上由水杨酸制备阿司匹林。

Esters can be hydrolysed by acid (reversible, yields carboxylic acid + alcohol) or by base (irreversible, yields carboxylate salt + alcohol). Base hydrolysis is called saponification and is used in soap manufacture from fats and oils.

酯可通过酸催化水解（可逆，生成羧酸 + 醇）或碱催化水解（不可逆，生成羧酸盐 + 醇）。碱催化水解称为皂化反应，用于从油脂制造肥皂。

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8. Amines | 胺

Amines are organic bases derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups. A primary amine has the general formula RNH₂.

胺是氨分子中一个或多个氢原子被烷基或芳基取代而得到的有机碱。伯胺的通式为 RNH₂。

The nitrogen atom in an amine has a lone pair of electrons, which can accept a proton, giving amines basic character. For example, CH₃NH₂ + H₂O ⇌ CH₃NH₃⁺ + OH⁻. Aliphatic amines are stronger bases than ammonia because the alkyl group donates electron density to nitrogen; aromatic amines (e.g., phenylamine) are weaker because the lone pair is delocalised into the benzene ring.

胺中氮原子有一对孤对电子，可接受质子，因此胺具有碱性。例如：CH₃NH₂ + H₂O ⇌ CH₃NH₃⁺ + OH⁻。脂肪胺的碱性比氨强，因为烷基向氮提供电子密度；芳香胺（如苯胺）的碱性较弱，因为孤对电子离域到苯环中。

Primary amines are prepared by reacting halogenoalkanes with excess ammonia in ethanol: C₂H₅Br + 2NH₃ → C₂H₅NH₂ + NH₄Br. Using excess amine, further substitution to secondary and tertiary amines occurs.

伯胺可通过卤代烷烃与过量氨在乙醇中反应制备：C₂H₅Br + 2NH₃ → C₂H₅NH₂ + NH₄Br。若使用过量胺，则进一步取代生成仲胺和叔胺。

Amines react with acyl chlorides to form N-substituted amides, useful in organic synthesis. Amines also react with H⁺ to form ammonium salts, which can be converted back with strong alkali.

胺与酰氯反应生成 N-取代酰胺，在有机合成中很有用。胺还可与 H⁺ 反应生成铵盐，铵盐可用强碱重新转化回胺。

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9. Aromatic Chemistry | 芳香化学

Benzene (C₆H₆) has a planar hexagonal structure with a delocalised system of π electrons: each carbon contributes one p-orbital electron to form a ring of electron density above and below the plane of the molecule. This delocalisation gives benzene extra stability (about 150 kJ/mol less energy than the hypothetical Kekulé structure) and explains why benzene undergoes substitution rather than addition.

苯（C₆H₆）具有平面六边形结构，拥有离域的 π 电子体系：每个碳原子贡献一个 p 轨道电子，在分子平面上下形成环状电子云。这种离域作用赋予苯额外的稳定性（比假设的 Kekulé 结构能量低约 150 kJ/mol），也解释了苯为何发生取代反应而不是加成反应。

The key aromatic reaction is electrophilic substitution, preserving the delocalised ring. Important examples:

芳香体系的关键反应是亲电取代，反应后保留离域环。重要实例如下：

• Nitration: benzene + conc HNO₃/H₂SO₄ → nitrobenzene + H₂O (50°C)

• 硝化：苯 + 浓 HNO₃/H₂SO₄ → 硝基苯 + H₂O（50°C）

• Halogenation: benzene + Br₂ with an AlBr₃ or FeBr₃ catalyst → bromobenzene + HBr

• 卤代：苯 + Br₂ 在 AlBr₃ 或 FeBr₃ 催化下 → 溴苯 + HBr

• Alkylation (Friedel-Crafts): benzene + RCl with AlCl₃ catalyst → alkylbenzene + HCl

• 烷基化（Friedel-Crafts）：苯 + RCl 在 AlCl₃ 催化下 → 烷基苯 + HCl

Phenol (C₆H₅OH) is more reactive than benzene toward electrophiles because the oxygen lone pair donates electron density into the ring, activating the 2- and 4-positions. Phenol is a weak acid (stronger than alcohols, weaker than carboxylic acids) and reacts with sodium hydroxide but not with sodium carbonate.

苯酚（C₆H₅OH）比苯对亲电试剂更活泼，因为氧的孤对电子向苯环供电子密度，活化 2 位和 4 位。苯酚是弱酸（酸性强于醇、弱于羧酸），可与氢氧化钠反应但不与碳酸钠反应。

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10. Polymers | 聚合物

Addition polymers are formed from alkene monomers containing a C=C double bond. The double bond opens and monomers join end-to-end, producing a saturated polymer chain with no other by-products. For example, ethene polymerises to poly(ethene); propene to poly(propene); vinyl chloride to PVC.

加成聚合物由含 C=C 双键的烯烃单体形成。双键打开，单体首尾相连生成饱和聚合物链，无其他副产物。例如：乙烯聚合成聚(乙烯)；丙烯生成聚(丙烯)；氯乙烯生成 PVC。

Condensation polymers form between bifunctional monomers with the elimination of a small molecule (usually water). Polyesters form from dicarboxylic acids and diols; polyamides form from dicarboxylic acids and diamines, or from amino acids. Examples include Terylene (polyester) and nylon (polyamide).

缩聚聚合物由双官能团单体之间反应形成，同时消除小分子（通常是水）。聚酯由二元羧酸和二醇形成；聚酰胺由二元羧酸和二胺形成，或由氨基酸形成。典型例子包括涤纶（聚酯）和尼龙（聚酰胺）。

Condensation polymers contain ester or amide linkages that can be hydrolysed, making

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