📚 Organic Chemistry Fundamentals for IGCSE WJEC | IGCSE WJEC 化学：有机化学基础考点精讲
Organic chemistry is the study of carbon-containing compounds, from simple fuels to complex biomolecules. In the IGCSE WJEC chemistry specification, you are expected to understand the basic principles of organic chemistry: how to name hydrocarbons, describe their reactions, and recognise key functional groups. Mastering these fundamentals will not only prepare you for the exam but also lay a strong foundation for further studies in chemistry.
有机化学是研究含碳化合物的学科，从简单燃料到复杂生物分子。在 IGCSE WJEC 化学考试大纲中，你需要理解有机化学的基本原理：如何命名碳氢化合物、描述它们的反应，并识别关键的官能团。掌握这些基础知识不仅有助于你应对考试，也为进一步学习化学打下坚实基础。
1. What is Organic Chemistry? | 什么是有机化学？
Organic chemistry is the branch of chemistry that focuses on compounds containing carbon, with the exception of carbonates, hydrogencarbonates, oxides of carbon and cyanides which are usually considered inorganic. The vast majority of organic compounds also contain hydrogen, and many include oxygen, nitrogen, or halogens. Carbon’s ability to form four covalent bonds and to catenate (link with other carbon atoms) makes the diversity of organic molecules possible.
有机化学是专注于含碳化合物（碳酸盐、碳酸氢盐、碳的氧化物和氰化物通常被视为无机物除外）的化学分支。绝大多数有机化合物还含有氢，许多还含有氧、氮或卤素。碳原子能够形成四个共价键并能够成链（与其他碳原子连接），使得有机分子的多样性成为可能。
In the IGCSE WJEC syllabus, organic chemistry includes the study of fossil fuels, alkanes, alkenes, and introduces functional groups such as alcohols and carboxylic acids. Understanding the sources and uses of organic compounds is also a core part of the specification.
在 IGCSE WJEC 大纲中，有机化学包括对化石燃料、烷烃、烯烃的研究，并介绍醇和羧酸等官能团。理解有机化合物的来源和用途也是大纲的核心部分。
2. The Unique Nature of Carbon | 碳的独特性质
Carbon has an atomic number of 6, with four electrons in its outer shell. This enables carbon to form four strong covalent bonds with other atoms, including other carbon atoms, leading to chains, branched structures, and rings. The bond energy of a C–C single bond is relatively high, making carbon skeletons stable under a wide range of conditions.
碳的原子序数为6，最外层有四个电子。这使得碳能够与其他原子（包括其他碳原子）形成四个强共价键，从而形成直链、支链结构和环状结构。C–C 单键的键能相对较高，使碳骨架在多种条件下保持稳定。
This catenation property is the reason why millions of organic compounds exist. In IGCSE, you only encounter relatively small organic molecules, but the same principles apply to giant molecules like polymers and biological macromolecules.
这种成链特性是数以百万计有机化合物存在的原因。在 IGCSE 阶段，你只接触相对较小的有机分子，但相同的原理也适用于聚合物和生物大分子等巨型分子。
3. Hydrocarbons: Alkanes and Alkenes | 烃：烷烃与烯烃
Hydrocarbons are the simplest organic compounds, consisting solely of carbon and hydrogen. They are divided into two main groups studied at IGCSE: alkanes and alkenes. Alkanes are saturated hydrocarbons containing only single C–C and C–H bonds. Alkenes are unsaturated hydrocarbons that contain at least one carbon–carbon double bond (C=C).
烃是最简单的有机化合物，仅由碳和氢组成。它们在 IGCSE 中被分为两个主要类别：烷烃和烯烃。烷烃是饱和烃，只含有 C–C 和 C–H 单键。烯烃是不饱和烃，至少含有一个碳碳双键（C=C）。
The general formula for alkanes is CₙH₂ₙ₊₂, and for alkenes with one double bond it is CₙH₂ₙ. This difference in hydrogen count reflects the unsaturation present in alkenes. You should be able to recognise and write molecular and structural formulae for both series up to about C₄ or C₅.
烷烃的通式为 CₙH₂ₙ₊₂，含有一个双键的烯烃通式为 CₙH₂ₙ。氢原子数量的差异反映了烯烃中的不饱和度。你应当能够识别并书写两种系列最多到约 C₄ 或 C₅ 的分子式与结构式。
4. 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 trend in physical properties. Each successive member differs from the previous one by a CH₂ unit. Both alkanes and alkenes form homologous series.
同系物是具有相同通式、相似化学性质以及物理性质渐变规律的一类有机化合物家族。每一个相邻成员相差一个 CH₂ 单元。烷烃和烯烃都构成同系物。
For example, in the alkane series, methane (CH₄), ethane (C₂H₆), propane (C₃H₈), and butane (C₄H₁₀) are consecutive members. Their boiling points increase as the molecular size increases due to stronger intermolecular forces. All alkanes undergo combustion and substitution reactions with halogens, demonstrating similar chemical behaviour.
例如，在烷烃系列中，甲烷 (CH₄)、乙烷 (C₂H₆)、丙烷 (C₃H₈) 和丁烷 (C₄H₁₀) 是相继的成员。随着分子尺寸增大，分子间作用力增强，它们的沸点逐渐升高。所有烷烃都会发生燃烧反应和与卤素的取代反应，展示了相似的化学行为。
5. Naming Organic Compounds (IUPAC) | 有机化合物的命名（IUPAC）
The International Union of Pure and Applied Chemistry (IUPAC) system provides a logical way to name organic molecules. For straight-chain alkanes, the name is based on the number of carbon atoms: meth- (1), eth- (2), prop- (3), but- (4), pent- (5). The suffix -ane indicates an alkane, while -ene indicates an alkene with a double bond.
国际纯粹与应用化学联合会（IUPAC）系统提供了一种命名的逻辑方法。对于直链烷烃，名称基于碳原子数：meth-（1）、eth-（2）、prop-（3）、but-（4）、pent-（5）。后缀 -ane 表示烷烃，而 -ene 表示含有双键的烯烃。
In alkenes, the position of the double bond is indicated by a number placed before the -ene suffix, such as but-1-ene or but-2-ene. When naming, number the carbon chain from the end closest to the double bond to give the lowest possible number to the functional group.
在烯烃中，双键的位置通过在 -ene 后缀前加数字表示，例如 but-1-ene 或 but-2-ene。命名时，从最靠近双键的一端开始给碳链编号，使官能团获得尽可能小的数字编号。
6. Structural Isomerism | 结构异构
Structural isomers are molecules that have the same molecular formula but different structural arrangements of atoms. This phenomenon is common in organic chemistry from C₄ onwards. For example, butane (C₄H₁₀) has two isomers: straight-chain butane and branched 2-methylpropane (isobutane).
结构异构体是指分子式相同但原子排列方式不同的分子。这种现象在有机化学中从 C₄ 开始很常见。例如，丁烷 (C₄H₁₀) 有两种异构体：直链丁烷和支链的 2-甲基丙烷（异丁烷）。
For alkenes, isomerism can also involve different positions of the double bond. Butene (C₄H₈) has three structural isomers: but-1-ene, but-2-ene, and 2-methylpropene. In the IGCSE WJEC exam, you may be asked to draw and name all possible structural isomers of a given molecular formula.
对于烯烃，异构现象还可能涉及双键位置的不同。丁烯 (C₄H₈) 有三种结构异构体：but-1-ene、but-2-ene 和 2-甲基丙烯。在 IGCSE WJEC 考试中，你可能需要画出并命名给定分子式的所有可能结构异构体。
7. Alkanes: Properties and Reactions | 烷烃的性质与反应
Alkanes are saturated hydrocarbons, generally unreactive due to strong C–C and C–H bonds. Their main reactions are combustion and substitution with halogens. Complete combustion of alkanes in excess oxygen produces carbon dioxide and water, releasing large amounts of energy, which is why they are used as fuels.
烷烃是饱和烃，由于牢固的 C–C 和 C–H 键通常不活泼。它们的主要反应是燃烧和与卤素的取代反应。烷烃在过量氧气中完全燃烧生成二氧化碳和水，释放大量能量，因此被用作燃料。
Example: CH₄ + 2O₂ → CO₂ + 2H₂O
Incomplete combustion occurs when oxygen is limited, producing carbon monoxide (toxic) or carbon (soot). Substitution with halogens requires ultraviolet light and results in the replacement of hydrogen atoms by halogen atoms, e.g., CH₄ + Cl₂ → CH₃Cl + HCl. This is a photochemical reaction.
在不完全燃烧中，氧气不足时会产生一氧化碳（有毒）或碳（烟灰）。与卤素的取代反应需要紫外光照射，氢原子被卤素原子取代，如 CH₄ + Cl₂ → CH₃Cl + HCl。这是一个光化学反应。
8. Alkenes: Properties and Reactions | 烯烃的性质与反应
Alkenes are unsaturated hydrocarbons containing a reactive C=C double bond. Their characteristic reaction is addition, where the double bond opens up and new atoms attach to the carbon atoms. Alkenes decolourise bromine water from orange-brown to colourless, which is the standard chemical test for unsaturation.
烯烃是不饱和烃，含有活泼的 C=C 双键。它们的特征反应是加成反应，双键打开，新的原子连接到碳原子上。烯烃能使溴水从橙棕色变为无色，这是检验不饱和度的标准化学测试。
Addition reactions with hydrogen (hydrogenation), steam (hydration), and halogens are important in industrial processes. For example, ethene reacts with steam in the presence of a phosphoric acid catalyst to produce ethanol: C₂H₄ + H₂O → C₂H₅OH. This is one method of manufacturing alcohol.
与氢气（加氢）、水蒸气（水合）和卤素的加成反应在工业生产中很重要。例如，乙烯在磷酸催化剂存在下与水蒸气反应生成乙醇：C₂H₄ + H₂O → C₂H₅OH。这是制造酒精的一种方法。
9. Cracking and its Importance | 裂解及其重要性
Cracking is a thermal decomposition process in which long-chain hydrocarbons from crude oil are broken down into shorter, more useful alkanes and alkenes. It helps match the supply of petroleum fractions with demand, as shorter-chain hydrocarbons are in higher demand for fuels and chemical feedstocks.
裂解是一种热分解过程，将原油中的长链烃断裂成较短、更有用的烷烃和烯烃。这有助于匹配石油馏分的供需，因为短链烃作为燃料和化工原料的需求量更大。
Two types of cracking: catalytic cracking uses a zeolite catalyst at moderate temperatures and pressures; steam cracking uses high temperature and steam without a catalyst. Both produce a mixture of alkanes and alkenes. The presence of C=C bonds in the products can be confirmed by the bromine water test.
裂解有两种类型：催化裂解在中等温度和压力下使用沸石催化剂；蒸汽裂解在高温和蒸汽下不使用催化剂。两者都产生烷烃和烯烃的混合物。产物中的 C=C 键可通过溴水试验确认。
10. Introduction to Functional Groups and Further Families | 官能团简介与其他系列
Beyond alkanes and alkenes, the IGCSE WJEC syllabus introduces two other homologous series: alcohols and carboxylic acids. A functional group is an atom or group of atoms that gives a compound its characteristic reactions. For alcohols, the functional group is –OH (hydroxyl); for carboxylic acids, it is –COOH (carboxyl).
除了烷烃和烯烃，IGCSE WJEC 大纲还介绍了另外两个同系物：醇和羧酸。官能团是赋予化合物特征反应的原子或原子团。对于醇，官能团是 –OH（羟基）；对于羧酸，官能团是 –COOH（羧基）。
Methanol, ethanol, propanol, and butanol are the first four members of the alcohol series. Ethanol is produced by fermentation of sugars or by hydration of ethene. Carboxylic acids, such as methanoic acid and ethanoic acid, are weak acids that react with metals, bases, and carbonates to form salts. Recognising these functional groups and their typical reactions is essential for exam success.
甲醇、乙醇、丙醇和丁醇是醇系列的前四个成员。乙醇可通过糖的发酵或乙烯的水合制得。羧酸，如甲酸和乙酸，是弱酸，能与金属、碱和碳酸盐反应生成盐。识别这些官能团及其典型反应对于考试成功至关重要。
11. Polymers from Alkenes | 烯烃聚合物
Addition polymerisation is a key reaction of alkenes, where many small alkene molecules (monomers) join together to form a long-chain polymer. Poly(ethene), poly(propene), and poly(chloroethene) (PVC) are common examples. The polymer is named by placing ‘poly’ in front of the monomer name.
加成聚合是烯烃的一个重要反应，许多小烯烃分子（单体）连接在一起形成长链聚合物。聚乙烯、聚丙烯和聚氯乙烯（PVC）是常见的例子。聚合物通过在单体名称前加“聚”字来命名。
The equation for polymerisation of ethene is often represented as n CH₂=CH₂ → –(–CH₂–CH₂–)–n. During the exam, you should be able to identify the monomer from a polymer repeat unit and vice versa. Understanding the structure and properties of addition polymers, including their lack of biodegradability, links to real-world environmental issues.
乙烯聚合的方程式常表示为 n CH₂=CH₂ → –(–CH₂–CH₂–)–n。在考试中，你应能从聚合物重复单元识别单体，反之亦然。理解加成聚合物的结构和性质，包括其难以生物降解的问题，与现实世界的环境问题紧密相连。
12. Key Experiments and Practical Skills | 关键实验与实操技能
In the IGCSE WJEC practical assessment, you may be asked about tests for unsaturation, combustion, or the preparation of ethene from ethanol. The decolourisation of bromine water is a simple qualitative test to distinguish alkenes from alkanes. Always remember to record colour changes and handle bromine water with care, as it is corrosive and toxic.
在 IGCSE WJEC 实验评估中，你可能会被问到关于不饱和度的测试、燃烧反应或从乙醇制备乙烯的实验。溴水褪色是区分烯烃和烷烃的简单定性测试。请务必记录颜色变化，并小心处理溴水，因为它具有腐蚀性和毒性。
Another key practical is the combustion of hydrocarbons: observing the sootiness of flame can indicate the carbon-to-hydrogen ratio. Alkenes tend to burn with a smokier flame than alkanes of similar size because of their higher carbon proportion. Such observations support qualitative analysis skills required by the specification.
另一个关键实验是烃的燃烧：观察火焰的烟灰程度可以指示碳氢比例。烯烃燃烧时往往比类似大小的烷烃产生更多黑烟，因为它们碳的比例更高。这类观察支持考试大纲所要求的定性分析技能。
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