📚 IGCSE Chemistry: Organic Chemistry Fundamentals Essentials | IGCSE 化学：有机化学基础考点精讲
Organic chemistry is the branch of chemistry that deals with the structure, properties and reactions of carbon-containing compounds. At IGCSE level, you are expected to master the fundamentals of homologous series, functional groups, naming conventions and the characteristic reactions of alkanes, alkenes, alcohols and carboxylic acids. This article covers all essential revision points to help you ace your exams.
有机化学是研究含碳化合物的结构、性质与反应的分支。在 IGCSE 阶段，你需要掌握同系物、官能团、命名规则以及烷烃、烯烃、醇和羧酸的特征反应等基础内容。本文梳理所有必考知识点，助你高效备考。
1. What is Organic Chemistry? | 什么是有机化学？
Organic chemistry focuses on compounds built around carbon atoms. With four valence electrons, carbon can form four covalent bonds, enabling it to create chains, branched structures and rings. Exceptions like carbon dioxide, carbonates and cyanides are classified as inorganic despite containing carbon.
有机化学专注于以碳原子为核心骨架的化合物。碳原子有四个价电子，能形成四个共价键，从而构成链状、支链和环状结构。然而，二氧化碳、碳酸盐和氰化物虽然含碳，却被视为无机物。
From fuels and plastics to pharmaceuticals and textiles, organic compounds are integral to daily life. The vast diversity stems from carbon’s ability to catenate—bond with itself to form stable long chains.
从燃料、塑料到药物和纺织品，有机化合物在日常生活中无处不在。这种多样性源于碳原子的自相结合能力——能形成稳定的长链——即“成链性”。
2. Homologous Series and Functional Groups | 同系物与官能团
A homologous series is a family of organic molecules that share the same functional group and a general formula. Members of the series exhibit similar chemical properties and show a gradual trend in physical properties, such as boiling points, as the carbon chain length increases.
同系物是一类具有相同官能团和通式的有机分子家族。该系列成员化学性质相似，而其物理性质（如沸点）随碳链增长呈现规律性变化。
The functional group is the reactive part of a molecule that determines its characteristic reactions. For example, the hydroxyl group (–OH) defines alcohols, while the carboxyl group (–COOH) defines carboxylic acids.
官能团是分子中的反应部分，决定了该物质的特征化学行为。例如，羟基 (–OH) 是醇的标志，而羧基 (–COOH) 是羧酸的标志。
| Homologous Series | Functional Group | General Formula |
|---|---|---|
| Alkanes | C–C (no specific group) | CₙH₂ₙ₊₂ |
| Alkenes | C=C | CₙH₂ₙ |
| Alcohols | –OH | CₙH₂ₙ₊₁OH (or CₙH₂ₙ₊₂O) |
| Carboxylic acids | –COOH | CₙH₂ₙ₊₁COOH (or CₙH₂ₙO₂) |
3. Naming Organic Compounds | 有机化合物的命名
IGCSE follows a systematic naming approach based on the number of carbon atoms in the longest continuous chain (prefix) and the functional group (suffix). The first four prefixes are meth- (1), eth- (2), prop- (3) and but- (4).
IGCSE 采用系统命名法，依据最长连续碳链的碳原子数选择前缀，并依据官能团选择后缀。前四个前缀分别是 meth- (1)、eth- (2)、prop- (3) 和 but- (4)。
To name an alkane, combine the prefix with ‘-ane’: methane, ethane, propane, butane. For alkenes, the suffix changes to ‘-ene’ (ethene, propene). Alcohols use ‘-anol’ (methanol, ethanol) and carboxylic acids use ‘-anoic acid’ (methanoic acid, ethanoic acid).
命名烷烃时，将前缀与 ‘-ane’ 结合：methane, ethane, propane, butane。烯烃后缀改为 ‘-ene’ (ethene, propene)；醇类后缀为 ‘-anol’ (methanol, ethanol)；羧酸后缀为 ‘-anoic acid’ (methanoic acid, ethanoic acid)。
When a compound has a functional group on a specific carbon, the number is placed before the suffix, e.g. propan-1-ol or propan-2-ol. Always number to give the functional group the lowest possible locant.
若官能团位于特定碳原子上，需在名称中插入位次数字，如 propan-1-ol 和 propan-2-ol。编号始终使官能团位次最小。
4. Alkanes: Saturated Hydrocarbons | 烷烃：饱和烃
Alkanes are saturated hydrocarbons with only single covalent bonds. Their general formula is CₙH₂ₙ₊₂. The simplest alkane is methane (CH₄). Because all bonds are fully occupied, alkanes are relatively unreactive, but they do undergo combustion and substitution reactions.
烷烃是只含有碳碳单键的饱和烃，通式为 CₙH₂ₙ₊₂。最简单的烷烃是甲烷 (CH₄)。由于所有价键饱和，烷烃相对不活泼，但可以发生燃烧反应和取代反应。
Complete combustion of alkanes in excess oxygen produces carbon dioxide and water, releasing a large amount of energy. For example:
CH₄ + 2O₂ → CO₂ + 2H₂O
完全燃烧时，烷烃与过量氧气反应生成二氧化碳和水，并释放大量能量。例如：
CH₄ + 2O₂ → CO₂ + 2H₂O
In the presence of ultraviolet light, alkanes react with halogens (e.g. chlorine) via a substitution reaction. A hydrogen atom is replaced by a halogen atom, forming a mixture of halogenoalkanes. For instance:
CH₄ + Cl₂ → CH₃Cl + HCl
在紫外光照射下，烷烃与卤素（如氯）发生取代反应，氢原子被卤素原子取代，生成卤代烷的混合物。例如：
CH₄ + Cl₂ → CH₃Cl + HCl
5. Alkenes: Unsaturated Hydrocarbons | 烯烃：不饱和烃
Alkenes contain at least one carbon-carbon double bond (C=C), making them unsaturated. Their general formula is CₙH₂ₙ. The double bond consists of a sigma bond and a pi bond, which gives the molecule restricted rotation and high reactivity.
烯烃至少含有一个碳碳双键 (C=C)，因而属于不饱和烃，通式为 CₙH₂ₙ。双键由一个 σ 键和一个 π 键组成，导致分子旋转受限且化学性质活泼。
The characteristic reaction of alkenes is addition, where the double bond opens to allow atoms or groups to attach. With bromine water (orange), an alkene decolourises it immediately, forming a dibromo compound. This is the standard test for unsaturation.
C₂H₄ + Br₂ → C₂H₄Br₂
烯烃的特征反应是加成反应，双键打开以接纳原子或基团。烯烃可使橙色溴水迅速褪色，生成二溴化合物，这是检验不饱和度的标准方法。
C₂H₄ + Br₂ → C₂H₄Br₂
Alkenes also undergo hydrogenation (addition of H₂ with a nickel catalyst) to form alkanes, and hydration (addition of steam with a phosphoric acid catalyst) to produce alcohols.
烯烃还能发生加氢反应（H₂，镍催化剂）生成烷烃，以及水合反应（水蒸气，磷酸催化剂）生成醇。
C₂H₄ + H₂ → C₂H₆
C₂H₄ + H₂O → C₂H₅OH
6. Alcohols: Structure and Reactions | 醇：结构与反应
Alcohols contain the hydroxyl functional group (–OH) attached to a carbon chain. The simplest alcohol is methanol (CH₃OH), but ethanol (C₂H₅OH) is the most commonly examined at IGCSE. Ethanol can be produced by fermentation of sugars (using yeast) or by hydration of ethene.
醇含有连接在碳链上的羟基 (–OH)。最简单的醇是甲醇 (CH₃OH)，但 IGCSE 最常考的是乙醇 (C₂H₅OH)。乙醇可通过糖类发酵（酵母）或乙烯水合法制取。
Fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ (conditions: yeast, 30–40°C, anaerobic). Hydration of ethene: C₂H₄ + H₂O → C₂H₅OH (phosphoric acid catalyst, 300°C, high pressure).
发酵：C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂（条件：酵母，30–40°C，厌氧）。乙烯水合：C₂H₄ + H₂O → C₂H₅OH（磷酸催化，300°C，高压）。
Alcohols burn readily in air, producing a clean blue flame:
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
醇在空气中燃烧充分，发出蓝色火焰：
C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
Oxidation of ethanol produces ethanoic acid. This can be achieved by heating with acidified potassium manganate(VII) or by the action of aerobic bacteria in air. The colour change from purple to colourless (manganate(VII) to Mn²⁺) confirms oxidation.
乙醇氧化生成乙酸（醋酸）。可用酸化高锰酸钾溶液加热氧化，或通过空气中的需氧微生物缓慢氧化实现。高锰酸钾由紫色变为无色（Mn²⁺）可证实氧化反应发生。
Reaction with sodium metal: ethanol reacts to form sodium ethoxide and hydrogen gas.
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
与金属钠反应：乙醇生成乙醇钠和氢气。
2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
7. Carboxylic Acids and Esters | 羧酸与酯
Carboxylic acids contain the –COOH functional group. They are weak acids, meaning they only partially ionise in water. Ethanoic acid (CH₃COOH) is the typical example at IGCSE. They react with metals, alkalis and carbonates to form salts, just like common inorganic acids, but at a slower rate.
羧酸含有羧基 (–COOH)，属于弱酸，在水中仅部分电离。IGCSE 常以乙酸 (CH₃COOH) 为例。羧酸同样能与金属、碱和碳酸盐发生典型酸反应生成盐，不过反应速率较慢。
Reaction with sodium carbonate: 2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O. Effervescence of CO₂ is observed.
与碳酸钠反应：2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O，可观察到 CO₂ 气泡产生。
Esterification is the reversible reaction between a carboxylic acid and an alcohol in the presence of a concentrated sulfuric acid catalyst. This produces an ester and water. Esters are responsible for fruity flavours and are used in fragrances and solvents.
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
酯化反应是羧酸与醇在浓硫酸催化下发生的可逆反应，生成酯和水。酯类物质具有果香，常用于香精和溶剂。
CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O
To name an ester, the alkyl group from the alcohol comes first (e.g. ethyl), and the acid part changes to ‘-anoate’ (ethanoate). So the product above is ethyl ethanoate.
酯的命名：醇的烷基部分在前（如 ethyl），酸的部分后缀改为 ‘-anoate’（如 ethanoate）。因此上述产物为 ethyl ethanoate（乙酸乙酯）。
8. Addition Polymerisation | 加成聚合反应
Addition polymerisation is the key reaction whereby many small unsaturated monomer molecules (alkenes) join together to form a long-chain polymer. The double bonds open up and link monomers without producing any other by-product.
加成聚合反应是许多不饱和小分子单体（烯烃）相互连接形成长链聚合物的核心反应。双键打开，单体依次连接，且不生成其他副产品。
Poly(ethene), commonly known as polythene, is produced from ethene under high pressure and temperature with an initiator. It is represented as –(CH₂–CH₂)–ₙ.
n CH₂=CH₂ → –(CH₂–CH₂)–ₙ
聚（乙烯）（俗称聚乙烯）由乙烯在高温高压和引发剂作用下制得，结构简式为 –(CH₂–CH₂)–ₙ。
n CH₂=CH₂ → –(CH₂–CH₂)–ₙ
Other important addition polymers include poly(propene) from propene, poly(chloroethene) (PVC) from chloroethene, and poly(tetrafluoroethene) (PTFE) from tetrafluoroethene. The repeating unit always retains the original atomic arrangement of the monomer, but with single bonds.
其他重要的加聚物包括聚丙烯（由丙烯制得）、聚氯乙烯（PVC，由氯乙烯制得）和聚四氟乙烯（PTFE，由四氟乙烯制得）。重复单元总是保留单体的原子排布，只是双键变为单键。
Disposal of addition polymers is challenging because they are non-biodegradable. IGCSE often links this to environmental impacts and recycling codes.
加聚物的废弃处理是一大难题，因为它们难以生物降解。IGCSE 常会联系其环境影响和回收标志进行考查。
9. Cracking and Fuels | 裂解与燃料
Cracking is the process of breaking long-chain alkane molecules from crude oil into smaller, more useful hydrocarbons. It is essential because demand for shorter-chain alkanes (petrol) and alkenes far exceeds their natural abundance in crude oil.
裂解是将原油中的长链烷烃分子断裂为更短、更有用的烃类的过程。由于市场对短链烷烃（汽油）和烯烃的需求远超过其在原油中的天然比例，裂解工艺不可或缺。
There are two main types: thermal cracking (high temperature, high pressure) and catalytic cracking (lower temperature and pressure with a zeolite catalyst). Both produce a mixture of alkanes and alkenes.
主要有两类：热裂解（高温高压）和催化裂解（较低温、低压，使用沸石催化剂）。两者产物均为烷烃和烯烃的混合物。
To confirm the presence of alkenes in the cracked product, the gaseous mixture can be bubbled through bromine water. Decolourisation from orange to colourless indicates alkene production.
为了验证裂解产物中有烯烃生成，可将气体混合物通入溴水。若橙色褪为无色，即证明有烯烃存在。
10. Summary of Key Reactions | 关键反应总结
The following table summarises the characteristic reactions you must recall for IGCSE Organic Chemistry. Understanding these patterns will allow you to predict products and answer extended questions confidently.
下表总结了 IGCSE 有机化学中必须掌握的特征反应。理解这些反应规律能帮助你预测产物并从容应对扩展题。
| Homologous Series | Reaction Type | Reagents / Conditions | Key Observations |
|---|---|---|---|
| Alkanes | Combustion | Excess O₂, ignition | CO₂ + H₂O, exothermic |
| Alkanes | Substitution | Halogen, UV light | Halogenoalkane mixture, steamy fumes of hydrogen halide |
| Alkenes | Addition (Br₂ test) | Bromine water, room temp | Orange → colourless |
| Alkenes | Hydrogenation | H₂, Ni catalyst, 150°C | Alkane produced |
| Alkenes | Hydration | Steam, H₃PO₄ catalyst, 300°C, high pressure | Alcohol produced |
| Alcohols | Combustion | Excess O₂, ignition | Clean blue flame, CO₂ + H₂O |
| Alcohols | Oxidation | Acidified KMnO₄, heat or aerobic bacteria | Purple → colourless; carboxylic acid formed |
| Carboxylic acids | Esterification | Alcohol, conc. H₂SO₄, heat | Fruity smell ester formed |
| Alkenes (monomer) | Addition polymerisation | High pressure, catalyst | Long-chain polymer (e.g. polythene) |
By linking structure to reactivity, IGCSE Organic Chemistry becomes a systematic story of how carbon-based molecules behave. Focus on functional group patterns, reaction conditions and observable changes to secure top marks.
将结构与反应性联系起来，IGCSE 有机化学就是一篇关于碳基分子行为的系统故事。紧紧抓住官能团规律、反应条件以及可观察到的变化，就能稳稳拿到高分。
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