📚 Functional Group Chemistry | 官能团化学
Organic chemistry is built around functional groups – specific atoms or bonds that dictate a molecule's chemical behaviour. Mastering their interconversions, typical reactions, and reaction mechanisms is essential for any IB Chemistry student aiming for top marks in Topic 10 and beyond.
有机化学的核心是官能团——决定分子化学性质的特定原子或键。掌握官能团之间的相互转化、典型反应和反应机理，是每个 IB 化学学生冲击高分的关键，尤其对 Topic 10 和后续内容至关重要。
1. Alkanes: Saturated Hydrocarbons | 烷烃：饱和烃
Alkanes have the general formula CₙH₂ₙ₊₂ and are saturated hydrocarbons containing only single C–C and C–H bonds. Their unreactivity is due to the high strength of σ bonds and low polarity.
烷烃的通式为 CₙH₂ₙ₊₂，是只含 C–C 和 C–H 单键的饱和烃。由于 σ 键强度高、极性低，烷烃一般化学性质不活泼。
Nevertheless, alkanes do undergo combustion, releasing large amounts of energy, and they react with halogens under UV light via a free‑radical substitution mechanism.
然而，烷烃可以燃烧释放大量能量，并在紫外光下与卤素发生自由基取代反应。
The radical chain reaction has three stages – initiation (homolytic fission of Cl₂ to form Cl• radicals), propagation (Cl• abstracts H from alkane, generating an alkyl radical which then reacts with Cl₂), and termination (radical combination).
自由基链式反应分三个阶段：引发（Cl₂ 均裂产生 Cl• 自由基）、增长（Cl• 夺取烷烃上的 H，生成的烷基自由基再与 Cl₂ 反应）和终止（自由基相互结合）。
Key example: CH₄ + Cl₂ (UV) → CH₃Cl + HCl, with further substitution possible.
关键示例：CH₄ + Cl₂ (UV) → CH₃Cl + HCl，还可能发生多取代。
2. Alkenes: Electrophilic Addition | 烯烃：亲电加成
ouble bond, consisting of one σ bond and one π bond. The π electrons make alkenes electron‑rich, inviting attack by electrophiles.
烯烃含有活泼的 C=C 双键，由一个 σ 键和一个 π 键组成。π 电子使烯烃富电子，容易受到亲电试剂的进攻。
Typical electrophilic addition reactions include addition of HX (HCl, HBr), halogens (Br₂), and water (steam with H₃PO₄ catalyst), as well as catalytic hydrogenation with H₂/Ni.
典型的亲电加成反应包括：与 HX（HCl、HBr）加成，与卤素（Br₂）加成，与水（H₃PO₄ 催化水蒸气）加成，以及用 H₂/Ni 催化加氢。
Markovnikov's rule guides the regioselectivity: when adding HX to an unsymmetrical alkene, the hydrogen attaches to the carbon with more hydrogens already, so the more stable carbocation intermediate forms.
马氏规则指导区域选择性：不对称烯烃与 HX 加成时，氢原子加到原本氢较多的碳上，从而形成更稳定的碳正离子中间体。
Addition of Br₂ dissolved in an organic solvent provides a useful test: the orange‑brown colour decolourises immediately, confirming unsaturation.
溴的四氯化碳溶液加成实验是一个有用的检测方法：橙棕色迅速褪去，证明分子中存在不饱和键。
3. Alcohols: Oxidation and Esterification | 醇：氧化与酯化
Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) based on the carbon bearing the –OH group. This classification determines their oxidation behaviour.
醇根据带有 –OH 的碳原子种类分为一级（1°）、二级（2°）和三级（3°），这一分类决定了它们的氧化行为。
Primary alcohols can be oxidised first to aldehydes using distilling off the aldehyde and then to carboxylic acids under reflux with excess acidified potassium dichromate(VI). Secondary alcohols oxidise to ketones, while tertiary alcohols resist oxidation.
一级醇可先氧化成醛（蒸馏分离产物），再在过量酸性重铬酸钾(VI)下回流氧化成羧酸。二级醇氧化成酮，三级醇则不易被氧化。
The colour change from orange (Cr₂O₇²⁻) to green (Cr³⁺) is a clear visual indicator of alcohol oxidation.
颜色由橙色（Cr₂O₇²⁻）变为绿色（Cr³⁺）是醇被氧化的明显标志。
Alcohols also react with carboxylic acids in the presence of concentrated H₂SO₄ to form esters – a condensation reaction known as Fischer esterification.
醇还可以在浓硫酸催化下与羧酸反应生成酯——这一缩合反应称为费歇尔酯化。
4. Halogenoalkanes: Nucleophilic Substitution | 卤代烷：亲核取代
Halogenoalkanes contain a polar C–X bond (X = F, Cl, Br, I), making the carbon atom electron‑deficient and susceptible to attack by nucleophiles such as OH⁻, NH₃, and CN⁻.
卤代烷含有极性的 C–X 键（X = F, Cl, Br, I），使碳原子缺电子，容易受到 OH⁻、NH₃ 和 CN⁻ 等亲核试剂的进攻。
Warm aqueous NaOH carries out hydrolysis, replacing the halogen with –OH to yield an alcohol. Heating with alcoholic ammonia produces amines via nucleophilic substitution, while reaction with KCN in ethanol extends the carbon chain to form nitriles.
温热 NaOH 水溶液水解卤代烷，卤原子被 –OH 取代生成醇。与氨的醇溶液共热得到胺，而与 KCN 乙醇溶液反应则增长碳链形成腈。
The rate of substitution depends on the halogenoalkane class: tertiary halogenoalkanes favour an SN1 mechanism via a carbocation intermediate, whereas primary ones usually proceed via an SN2 bimolecular pathway.
取代速率与卤代烷的类别有关：三级卤代烷倾向于通过碳正离子中间体的 SN1 机理，一级卤代烷通常按双分子 SN2 途径进行。
5. Aldehydes and Ketones: The Carbonyl Group | 醛和酮：羰基化合物
e at least one hydrogen attached to the carbonyl carbon, making them more easily oxidised.
醛和酮都含有极性的 C=O 基团，但醛的羰基碳上至少连有一个氢原子，因此更容易被氧化。
Aldehydes can be oxidised to carboxylic acids by mild oxidising agents like Tollens' reagent (silver mirror) or Fehling's solution (brick‑red precipitate), while ketones give no reaction – these tests distinguish between the two.
醛可被 Tollens 试剂（银镜反应）或 Fehling 溶液（砖红色沉淀）等温和氧化剂氧化为羧酸，而酮不发生反应——这些测试可用于区别醛和酮。
Both aldehydes and ketones undergo nucleophilic addition, for example with HCN to form hydroxynitriles (cyanohydrins), a reaction that extends the carbon chain.
醛和酮均可发生亲核加成，例如与 HCN 反应生成羟基腈（氰醇），这是一个增长碳链的反应。
Reduction with NaBH₄ (in water or ethanol) or LiAlH₄ (in dry ether) converts aldehydes to primary alcohols and ketones to secondary alcohols.
用 NaBH₄（水或乙醇溶液）或 LiAlH₄（干燥乙醚）还原，可将醛转化为一级醇，酮转化为二级醇。
6. Carboxylic Acids: Acidity and Derivatives | 羧酸：酸性及其衍生物
Carboxylic acids contain the –COOH group and are weak acids, partially dissociating in water to give H₃O⁺ and a carboxylate ion, which is resonance stabilised.
羧酸含有 –COOH 基团，是弱酸，在水中部分电离生成 H₃O⁺ 和羧酸根离子，后者因共振而稳定。
They react with reactive metals to produce hydrogen gas, with bases to form salts, and with carbonates to release CO₂ – typical acid behaviour.
羧酸可与活泼金属反应放出氢气，与碱反应成盐，与碳酸盐反应释放 CO₂——体现了典型的酸的性质。
Carboxylic acids can be reduced to primary alcohols by LiAlH₄, and they form esters, acyl halides, and amides as important derivatives, though acyl chlorides and amides are often introduced via more reactive intermediates.
羧酸可被 LiAlH₄ 还原为一级醇，并且可以转化为酯、酰卤和酰胺等重要衍生物，不过酰氯和酰胺常需通过更活泼的中间体来制备。
7. Esters: Sweet‑Smelling Compounds | 酯：芳香族化合物（气味芬芳）
Esters are formed by the condensation reaction between a carboxylic acid and an alcohol, catalysed by concentrated sulfuric acid, with water as the by‑product.
酯由羧酸与醇在浓硫酸催化下通过缩合反应生成，同时产生水。
They have characteristic fruity or floral odours and are widely used as fragrances, flavourings, and solvents. The ester link –COO– is the functional group.
酯具有独特的水果或花香气味，广泛用作香料、调味剂和溶剂。官能团是 –COO– 酯键。
Esters can be hydrolysed back to the parent acid and alcohol either under acidic conditions (reversible) or under alkaline conditions (irreversible, producing the carboxylate salt – saponification).
酯可在酸性条件下水解回到母体酸和醇（可逆），也可在碱性条件下水解（不可逆，生成羧酸盐——皂化反应）。
8. Amines: Basic Nitrogen Compounds | 胺：含氮碱性化合物
Amines are organic derivatives of ammonia, classified as primary, secondary, or tertiary depending on the number of alkyl/aryl groups attached to nitrogen.
胺是氨的有机衍生物，根据氮上连接的烷基/芳基数目分为一级、二级和三级胺。
The lone pair on nitrogen makes amines both basic (proton acceptors) and nucleophilic. They react with acids to form ammonium salts, which are ionic and water‑soluble.
氮原子上的孤对电子赋予胺碱性（质子接受体）和亲核性。胺与酸反应生成铵盐，是离子型且溶于水。
Primary amines can be prepared by nucleophilic substitution of halogenoalkanes with excess ammonia or by reduction of nitriles and amides.
一级胺可通过卤代烷与过量氨的亲核取代反应，或通过还原腈和酰胺来制备。
9. Nitriles and Amides: Nitrogen‑containing Functional Groups | 腈与酰胺：含氮官能团
Nitriles contain the –C≡N group and can be hydrolysed under acidic or basic conditions to yield carboxylic acids (or carboxylate salts), effectively adding one carbon atom to the chain.
腈含有 –C≡N 基团，可在酸或碱条件下水解生成羧酸（或羧酸盐），从而有效地在碳链上增加一个碳原子。
Reduction of a nitrile with LiAlH₄ or catalytic hydrogenation yields a primary amine, providing a valuable synthetic route to amines.
用 LiAlH₄ 或催化加氢还原腈可得到一级胺，这是一条重要的胺合成路线。
Amides contain the –CONH₂ group and can be dehydrated to nitriles using P₄O₁₀; they are also formed when acyl chlorides react with ammonia or amines. Hydrolysis of amides produces carboxylic acids and ammonia (or amines).
酰胺含有 –CONH₂ 基团，可用 P₄O₁₀ 脱水生成腈；酰氯与氨或胺反应也可制得酰胺。酰胺水解生成羧酸和氨（或胺）。
10. Benzene and Electrophilic Substitution | 苯与亲电取代
Benzene (C₆H₆) is an aromatic compound with a delocalised π‑electron system above and below the ring, giving it exceptional stability and a reluctance to undergo addition reactions.
苯（C₆H₆）是一种芳香族化合物，环的上方和下方形成离域 π 电子系统，具有特殊的稳定性，不易发生加成反应。
Instead, benzene undergoes electrophilic aromatic substitution, where an electrophile replaces a hydrogen atom on the ring while the aromatic system is preserved.
苯通常发生亲电芳香取代反应，亲电试剂取代环上的氢原子，同时保留芳香体系。
Key examples include nitration (HNO₃/H₂SO₄, forming nitrobenzene), halogenation (Br₂/FeBr₃ or Cl₂/AlCl₃), and Friedel–Crafts alkylation and acylation, all requiring a catalyst to generate the strong electrophile.
重要示例包括硝化（HNO₃/H₂SO₄，生成硝基苯）、卤化（Br₂/FeBr₃ 或 Cl₂/AlCl₃），以及傅–克烷基化和酰基化反应，均需催化剂生成强亲电试剂。
Although reluctant, benzene can be hydrogenated under high pressure with a nickel catalyst to form cyclohexane, demonstrating that addition is possible only under forcing conditions.
尽管苯不易加成，但在高压和镍催化剂下仍可加氢生成环己烷，表明只有在剧烈条件下苯才能发生加成反应。
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