📚 IGCSE CIE Chemistry: Organic Chemistry Fundamentals Exam Tips | IGCSE CIE 化学：有机化学基础考点精讲
Organic chemistry is the study of carbon compounds, excluding carbonates, oxides and cyanides. For IGCSE CIE Chemistry, mastering the basics means knowing how to name and draw molecules, recognise functional groups, predict reactions and understand the properties of different homologous series. This revision guide covers all the core fundamentals you need to excel in Paper 2, 4 and 6.
有机化学是研究碳化合物的学科，但不包括碳酸盐、氧化物和氰化物。对 IGCSE CIE 化学而言，打好基础意味着你必须掌握如何命名与画出分子结构、识别官能团、预测反应并理解不同同系物的性质。本文梳理了核心考点，助你在试卷 2、4、6 中稳稳得分。
1. What is Organic Chemistry? | 什么是有机化学？
Organic chemistry focuses on compounds that contain carbon atoms covalently bonded to hydrogen, oxygen, nitrogen and other elements. Carbon can form four covalent bonds, allowing it to make long chains, branched structures and rings.
有机化学的研究对象是含有碳原子的化合物，碳通常与氢、氧、氮等元素以共价键结合。碳原子可以形成四个共价键，因此能够构筑长链、支链和环状结构。
The simplest organic molecules are hydrocarbons: compounds made only of carbon and hydrogen. Methane (CH₄) is the simplest hydrocarbon. The ability of carbon to catenate (bond to itself) is the reason for the vast number of organic compounds.
最简单的有机分子是烃——仅由碳和氢组成的化合物。甲烷（CH₄）是最简单的烃。碳原子能够相互连接（成链），这使得有机化合物的种类极其繁多。
2. Hydrocarbons: Alkanes and Alkenes | 烃：烷烃与烯烃
The two main hydrocarbon families you must know are alkanes and alkenes. Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂. They contain only single covalent bonds (C–C and C–H). Methane, ethane (C₂H₆) and propane (C₃H₈) are typical alkanes.
你必须掌握的两大烃族是烷烃和烯烃。烷烃是饱和烃，通式为 CₙH₂ₙ₊₂，分子中只含单键（C–C 和 C–H）。典型的烷烃有甲烷、乙烷（C₂H₆）和丙烷（C₃H₈）。
Alkenes are unsaturated hydrocarbons with the general formula CₙH₂ₙ. They contain at least one carbon–carbon double bond (C=C). Ethene (C₂H₄) and propene (C₃H₆) are the simplest alkenes. The double bond is the functional group that makes alkenes much more reactive than alkanes.
烯烃是不饱和烃，通式为 CₙH₂ₙ，分子中至少含有一个碳碳双键（C=C）。最简单的烯烃是乙烯（C₂H₄）和丙烯（C₃H₆）。双键是烯烃的官能团，使得烯烃的反应活性远高于烷烃。
3. Homologous Series | 同系物
A homologous series is a family of organic compounds with the same general formula, similar chemical properties and a gradual change in physical properties. Alkanes and alkenes are examples. Each successive member differs by a –CH₂– unit.
同系物是一类具有相同通式、化学性质相似且物理性质呈规律性变化的有机化合物家族。烷烃和烯烃就是典型的同系物。相邻成员之间相差一个 –CH₂– 单元。
As the carbon chain length increases, boiling points and viscosity rise, while flammability decreases. This trend is due to increasing intermolecular forces (London dispersion forces) between larger molecules.
随着碳链增长，同系物的沸点和粘度升高，可燃性下降。这是因为分子变大，分子间作用力（伦敦色散力）增强。
4. IUPAC Naming Rules | IUPAC 命名规则
Systematic naming follows IUPAC rules: identify the longest continuous carbon chain to give the stem name (meth-, eth-, prop-, but-, pent-, hex-), then add the suffix –ane for alkanes or –ene for alkenes. Numbers indicate the position of the double bond or side chains.
系统命名遵循 IUPAC 规则：先找出最长的连续碳链，确定母体名称（甲、乙、丙、丁、戊、己），然后烷烃加后缀 –ane，烯烃加 –ene。用数字标明双键或取代基的位置。
For example, CH₃–CH₂–CH=CH₂ is but-1-ene, not but-3-ene, because the double bond should have the lowest possible number. Side chains like methyl (–CH₃) or ethyl (–C₂H₅) are listed in alphabetical order with position numbers.
例如，CH₃–CH₂–CH=CH₂ 应命名为丁-1-烯，而非丁-3-烯，因为双键编号应尽可能小。甲基（–CH₃）或乙基（–C₂H₅）等取代基要按照字母顺序列出，并标明位置。
5. Isomerism | 同分异构
Isomers are compounds with the same molecular formula but different structural formulas. In IGCSE, you need to recognise chain isomers and position isomers. For instance, butane (C₄H₁₀) has a straight-chain form and a branched isomer called 2-methylpropane.
同分异构体是指分子式相同但结构式不同的化合物。IGCSE 要求你识别碳链异构和位置异构。例如，丁烷（C₄H₁₀）有直链形式和支链异构体 2-甲基丙烷。
Alkenes also show position isomerism: but-1-ene and but-2-ene both have the formula C₄H₈ but differ in the position of the double bond. Drawing displayed formulas clearly helps you score full marks in naming questions.
烯烃也会出现位置异构：丁-1-烯和丁-2-烯的分子式都是 C₄H₈，但双键位置不同。清晰地画出结构式有助于在命名题中拿到满分。
6. Combustion of Hydrocarbons | 烃的燃烧
Hydrocarbons burn in excess oxygen to produce carbon dioxide and water. This is complete combustion. The word equation for methane is: methane + oxygen → carbon dioxide + water. The balanced symbol equation is CH₄ + 2O₂ → CO₂ + 2H₂O.
烃在过量氧气中燃烧生成二氧化碳和水，这是完全燃烧。甲烷燃烧的文字方程式为：甲烷 + 氧气 → 二氧化碳 + 水。配平的符号方程式为 CH₄ + 2O₂ → CO₂ + 2H₂O。
In a limited supply of oxygen, incomplete combustion occurs, producing carbon monoxide (toxic) or carbon (soot) along with water. Carbon monoxide is dangerous because it binds irreversibly to haemoglobin, reducing the blood’s oxygen-carrying capacity.
在氧气不足时会发生不完全燃烧，生成一氧化碳（有毒）或碳（黑烟）以及水。一氧化碳很危险，因为它会与血红蛋白不可逆结合，降低血液的携氧能力。
7. Addition Reactions of Alkenes | 烯烃的加成反应
The C=C double bond makes alkenes reactive. They undergo addition reactions, where the double bond opens up and atoms add across it. The product is a single saturated molecule.
C=C 双键使烯烃很活泼。它们发生加成反应，双键打开，原子加到双键两端，生成一个饱和分子。
Two key examples: (1) Reaction with bromine – ethene reacts with brown bromine water, turning it colourless. This is the test for unsaturation. The product is 1,2-dibromoethane. (2) Hydrogenation – ethene reacts with hydrogen (with a nickel catalyst at about 150 °C) to form ethane. This is used to harden vegetable oils into margarine.
两个关键实例：(1) 与溴反应——乙烯与棕色的溴水反应，使溴水褪色，这就是不饱和性的检验方法，产物是 1,2-二溴乙烷。(2) 加氢反应——乙烯与氢气（镍催化，150 °C 左右）反应生成乙烷，该反应用于将植物油硬化制成人造黄油。
8. Addition Polymerisation | 加成聚合
Small alkene molecules (monomers) can join together under high pressure and with a catalyst to form long polymer chains. This is addition polymerisation. No other products are formed.
小分子烯烃（单体）在高压和催化剂作用下可以相互连接，形成长链聚合物，这便是加成聚合，反应中没有其他产物生成。
For example, poly(ethene) is made from ethene monomers. The repeating unit is –CH₂–CH₂–. The equation can be written as: n CH₂=CH₂ → –(CH₂–CH₂)–ₙ. Poly(propene) and poly(chloroethene) (PVC) are other common addition polymers. Be prepared to draw the polymer repeating unit given the monomer, or vice versa.
例如，聚乙烯由乙烯单体聚合而成，重复单元为 –CH₂–CH₂–。方程式可写为：n CH₂=CH₂ → –(CH₂–CH₂)–ₙ。聚丙烯和聚氯乙烯（PVC）也是常见的加成聚合物。考试中可能会要求你根据单体画出聚合物重复单元，或反过来。
9. Alcohols: Making Ethanol | 醇：乙醇的制备
Alcohols contain the hydroxyl functional group (–OH). Ethanol (C₂H₅OH) is the most familiar. Two methods of production are tested: fermentation of sugars (glucose → ethanol + carbon dioxide, using yeast at 30 °C) and hydration of ethene (C₂H₄ + H₂O → C₂H₅OH, with phosphoric acid catalyst at 300 °C and high pressure).
醇含有羟基官能团（–OH）。最熟悉的是乙醇（C₂H₅OH）。需要掌握的两种制备方法是：糖的发酵（葡萄糖在酵母作用下，30 °C 生成乙醇和二氧化碳）和乙烯水化（C₂H₄ + H₂O → C₂H₅OH，磷酸催化，300 °C，高压）。
Fermentation is a batch process that uses renewable resources (sugarcane, corn) but produces a dilute ethanol solution. Hydration of ethene gives a continuous process with a purer product but requires non-renewable crude oil. Ethanol burns with a clean blue flame and can be oxidised to ethanoic acid.
发酵是间歇式过程，使用可再生原料（甘蔗、玉米），但得到的是稀乙醇溶液。乙烯水化是连续过程，产物较纯，但需要不可再生的原油。乙醇燃烧产生淡蓝色火焰，还可被氧化成乙酸。
10. Carboxylic Acids | 羧酸
Carboxylic acids have the functional group –COOH. They are weak acids, partially ionising in water. Ethanoic acid (CH₃COOH) is the typical example. It reacts with metals, bases and carbonates to form salts, just like mineral acids, but more slowly.
羧酸含有官能团 –COOH。它们是弱酸，在水中部分电离。典型的羧酸是乙酸（CH₃COOH）。它与金属、碱和碳酸盐反应生成盐，反应模式与无机酸相似，但速率较慢。
Vinegar is a dilute solution of ethanoic acid. The reaction with ethanol (in the presence of an acid catalyst) produces esters, which have fruity smells and are used in flavourings and perfumes. Although esterification may be touched on at IGCSE, you should know that ethanoic acid and ethanol form ethyl ethanoate and water.
食醋是乙酸的稀溶液。乙酸与乙醇（在酸催化下）反应生成酯，酯有果香味，常用于调味剂和香水。虽然酯化反应在 IGCSE 可能只是简单提及，但你应知道乙酸和乙醇反应生成乙酸乙酯和水。
11. Cracking | 裂解
Cracking breaks long-chain alkanes from crude oil into smaller, more useful alkanes and alkenes. It is a thermal decomposition reaction, carried out with a catalyst (catalytic cracking) or at high temperature with steam (steam cracking).
裂解将来自原油的长链烷烃断裂成较短、更有用的烷烃和烯烃。这是一种热分解反应，可使用催化剂（催化裂解）或在高温蒸汽下进行（蒸汽裂解）。
The products include fuels like petrol and alkenes for making polymers. Cracking helps meet the higher demand for shorter-chain hydrocarbons. In an exam, you may be asked to write an equation showing one molecule of a long alkane producing a shorter alkane and an alkene, e.g., C₁₀H₂₂ → C₅H₁₂ + C₃H₆ + C₂H₄ (not balanced necessarily, but atom count must match).
产物包括汽油等燃料和用于制造聚合物的烯烃。裂解有助于满足对短链烃的高需求。考试中可能要求写出一个长链烷烃裂解生成一个短链烷烃和一个烯烃的方程式，例如 C₁₀H₂₂ → C₅H₁₂ + C₃H₆ + C₂H₄（不一定配平，但原子数必须守恒）。
12. Exam Tips Summary | 考点总结
When drawing structures, show every atom and every bond. Use displayed formulas unless the question specifically asks for a skeletal formula (rare at IGCSE). Label the double bond clearly in alkenes.
在画结构时，要展示出每一个原子和每一个键，除非题目特别要求（IGCSE 极少要求骨架式），一律使用展示式。烯烃中的双键要画清楚。
Learn the difference between ’empirical formula’, ‘molecular formula’ and ‘displayed formula’. Always write the number of the carbon atom where the functional group is attached when naming branched or unsaturated molecules. For addition polymerisation, make sure your repeating unit has the correct bonds extending out of the brackets.
区分清楚实验式、分子式和展示式的区别。命名含支链或不饱和分子时，始终标明官能团所在碳原子的编号。对于加成聚合，要确保重复单元有正确的延伸键伸出括号外。
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