📚 Organic Chemistry Basics: Key Points for OCR IGCSE Chemistry | 有机化学基础：OCR IGCSE 化学考点精讲
Organic chemistry is a core topic in the OCR IGCSE Chemistry syllabus, exploring the vast world of carbon-based compounds. This article condenses the essential concepts, from homologous series and functional groups to the reactions of alkanes, alkenes, alcohols, carboxylic acids and polymers, to help you build confidence and accuracy in exams.
有机化学是 OCR IGCSE 化学考试大纲中的核心主题，探索碳基化合物的广阔世界。本文凝练了必考概念，从同系物和官能团到烷烃、烯烃、醇、羧酸及聚合物的反应，帮助你建立考试的信心与精准度。
1. What is Organic Chemistry? | 什么是有机化学？
Organic chemistry is the study of carbon-containing compounds, with a few exceptions such as carbon oxides (CO, CO₂), carbonates (e.g. CaCO₃), hydrogencarbonates and cyanides. Carbon atoms form four strong covalent bonds, enabling the formation of chains, branched structures and rings, which gives rise to millions of organic molecules.
有机化学是研究含碳化合物的学科，但少数物质除外，如一氧化碳、二氧化碳、碳酸盐（如碳酸钙）、碳酸氢盐及氰化物。碳原子能形成四个强共价键，从而构成链状、支链及环状结构，造就了数以百万计的有机分子。
In the OCR exam, you will be expected to recognise organic compounds by their molecular structures, identify functional groups and predict chemical behaviour. A strong grasp of basic terminology such as saturated, unsaturated, hydrocarbon and functional group is the first step to success.
在 OCR 考试中，你需要根据分子结构辨识有机化合物、识别官能团并预测化学性质。牢固掌握饱和、不饱和、烃、官能团等基础术语是成功的第一步。
All organic compounds contain carbon atoms bonded to other elements, most commonly hydrogen, oxygen, nitrogen and halogens. The carbon–carbon bond is particularly stable, making catenation possible – the ability of carbon atoms to link together to form long chains.
所有有机化合物都含有碳原子，通常与氢、氧、氮和卤素等其他元素键合。碳-碳键尤其稳定，使得碳原子能够自相结合成链，即碳链结合能力。
2. Homologous Series and Functional Groups | 同系物与官能团
A homologous series is a family of organic compounds with the same general formula, similar chemical properties, and a gradation in physical properties (e.g. increasing boiling points with chain length). Each consecutive member differs by a CH₂ unit.
同系物是一类具有相同通式、相似化学性质且物理性质呈规律性递变（如随碳链增长沸点升高）的有机化合物家族。每一个相邻成员之间相差一个 CH₂ 单元。
The chemical reactions of a homologous series are determined by its functional group – m or group of atoms that gives the molecule its characteristic reactions. For example, the – kes them react similarly, while the C=C bond in alkenes dictates their addition chemistry.
同系物的化学反应由官能团决定——官能团是赋予分子特征反应的原子或原子团。例如，醇中的 –OH 基团使它们反应相似，而烯烃中的 C=C 双键则决定了它们的加成化学。
Below are the key homologous series you must know for OCR IGCSE:
以下是你必须掌握的 OCR IGCSE 关键同系物：
, functional group C=C, unsaturated. Alcohols: general formula CₙH₂ₙ₊₁OH, functional group –OH. Carboxylic acids: general formula CₙH₂ₙ₊₁COOH, functional group –COOH. Esters: formed from alcohol and carboxylic acid, functional group –COO–.
烷烃：通式 CₙH₂ₙ₊₂，无官能团，饱和烃。烯烃：通式 CₙH₂ₙ，官能团 C=C，不饱和烃。醇：通式 CₙH₂ₙ₊₁OH，官能团 –OH。羧酸：通式 CₙH₂ₙ₊₁COOH，官能团 –COOH。酯：由醇和羧酸形成，官能团 –COO–。
3. Naming Alkanes | 烷烃的命名
The names of alkanes follow a simple pattern using prefixes that indicate the number of carbon atoms: meth- (1), eth- (2), prop- (3), but- (4). Combined with the suffix -ane, we get methane, ethane, propane and butane. Beyond butane, systematic naming continues with pent- (5), hex- (6), but for IGCSE the focus is usually up to four carbons.
烷烃的命名采用简单的规则，前缀表示碳原子数：meth-（1个）、eth-（2个）、prop-（3个）、but-（4个）。加上后缀 -ane，就得到甲烷、乙烷、丙烷和丁烷。丁烷之后系统命名还采用 pent-（5）、hex-（6），但在 IGCSE 阶段通常要求掌握到四个碳。
Structural formulas illustrate the full arrangement of atoms. Methane (CH₄) has one carbon bonded to four hydrogens. Ethane (CH₃CH₃ or C₂H₆) has a C–C single bond. Propane (CH₃CH₂CH₃) and butane (CH₃CH₂CH₂CH₃) extend the chain further. The displayed formula shows every atom and bond clearly, which is often required in exam answers.
结构式展示原子的完整排列。甲烷（CH₄）由一个碳原子与四个氢原子键合。乙烷（CH₃CH₃ 或 C₂H₆）含有一个 C–C 单键。丙烷（CH₃CH₂CH₃）和丁烷（CH₃CH₂CH₂CH₃）进一步延伸碳链。完整显示式清楚地标出所有原子和键，通常在考试答题中要求给出。
4. Chemical Properties of Alkanes | 烷烃的化学性质
Alkanes are relatively unreactive due to the strong C–C and C–H bonds, but they undergo two key reactions for the exam: combustion and substitution with halogens.
烷烃由于 C–C 键和 C–H 键牢固，相对不活泼，但考试中涉及两个核心反应：燃烧及与卤素的取代反应。
Complete combustion of alkanes in plenty of oxygen produces carbon dioxide and water, releasing large amounts of heat. For methane:
烷烃在充足氧气中完全燃烧生成二氧化碳和水，并释放大量热能。以甲烷为例：
CH₄ + 2O₂ → CO₂ + 2H₂O
Incomplete combustion occurs when oxygen is limited, forming poisonous carbon monoxide (CO) or carbon (soot). This is a safety concern with gas appliances, and you must be able to write related equations.
氧气不足时发生不完全燃烧，生成有毒的一氧化碳（CO）或碳（炭黑）。这是燃气设备的安全隐患，你必须能够书写相关方程式。
The substitution reaction with chlorine or bromine requires ultraviolet light. A hydrogen atom is replaced by a halogen atom. For methane and chlorine:
与氯或溴的取代反应需要紫外光照。一个氢原子被卤素原子取代。以甲烷和氯气为例：
CH₄ + Cl₂ → CH₃Cl + HCl
Further substitution can occur, producing dichloromethane, trichloromethane and tetrachloromethane, but at IGCSE level recognising the principle is the focus.
进一步取代可生成二氯甲烷、三氯甲烷和四氯化碳，但在 IGCSE 层面重在理解原理。
5. Alkenes: Structure and the C=C Bond | 烯烃：结构与碳碳双键
Alkenes are unsaturated hydrocarbons containing at least one carbon– l formula is CₙH₂ₙ. The presence of the double bond makes them far more reactive than alkanes, as the π bond can break easily to allow addition.
烯烃是不饱和烃，至少含有一个碳碳双键（C=C）。通式为 CₙH₂ₙ。双键的存在使它们比烷烃活泼得多，因为 π 键容易断裂，从而发生加成反应。
the suffix -ene. In drawn structures you must show the double bond clearly, e.g. CH₂=CH₂.
乙烯（C₂H₄）和丙烯（C₃H₆）是最简单的烯烃。它们的命名遵循与烷烃相同的前缀规则，但后缀为 -ene。绘制结构时必须清晰表示双键，如 CH₂=CH₂。
A key test for unsaturation is the addition of bromine water. Alkenes rapidly decolourise orange bromine water, while alkanes do not react in the dark. This is a distinctive test-tube reaction you will need to describe and explain.
不饱和键的关键检验是溴水加成。烯烃能迅速使橙色溴水褪色，而烷烃在黑暗环境中则不反应。这是你必须会描述和解释的特征试管反应。
6. Addition Reactions of Alkenes | 烯烃的加成反应
ens up, and new atoms attach to the carbons, converting the unsaturated alkene into a saturated compound.
加成反应是碳碳双键的特征反应。双键打开，新原子连接到碳上，将不饱和烯烃转化为饱和化合物。
Addition of hydrogen (hydrogenation) converts alkenes to alkanes using a nickel catalyst at about 150 °C. For ethene:
加氢（氢化）在约 150 °C 和镍催化剂作用下将烯烃转化为烷烃。以乙烯为例：
C₂H₄ + H₂ → C₂H₆
Addition of steam (hydration) produces alcohols directly. Ethene reacts with steam at 300 °C and 60 atm pressure over a phosphoric acid catalyst to form ethanol. This is a reversible reaction, so an equilibrium mixture is obtained.
水蒸气加成（水合）直接生成醇。乙烯与水蒸汽在 300 °C、60 大气压、磷酸催化剂条件下反应生成乙醇。这是一个可逆反应，因此得到的是平衡混合物。
C₂H₄ + H₂O ⇌ C₂H₅OH
Addition of halogens, such as bromine, occurs readily at room temperature without a catalyst. With bromine, the product is a dibromoalkane:
卤素加成反应，如与溴反应，在室温下无需催化剂即可快速进行。与溴反应生成二溴代烷：
C₂H₄ + Br₂ → C₂H₄Br₂
7. Alcohols: The Hydroxyl Group | 醇：羟基
Alcohols contain the functional group –OH (hydroxyl) attached to a carbon chain. Their general formula is CₙH₂ₙ₊₁OH. The simplest are methanol (CH₃OH) and ethanol (CH₃CH₂OH). Propanol exists as two isomers: propan-1-ol (CH₃CH₂CH₂OH) and propan-2-ol (CH₃CH(OH)CH₃).
醇含有连接在碳链上的官能团 –OH（羟基），通式为 CₙH₂ₙ₊₁OH。最简单的醇是甲醇（CH₃OH）和乙醇（CH₃CH₂OH）。丙醇有两种同分异构体：丙-1-醇（CH₃CH₂CH₂OH）和丙-2-醇（CH₃CH(OH)CH₃）。
Ethanol can be produced by fermentation of sugars using yeast at around 30 °C, an anaerobic process. Industrially, it is also made by hydration of ethene as described above. A comparison of the two methods in terms of raw materials, rate and purity is a common exam question.
乙醇可由酵母在约 30 °C 发酵糖类得到，是一个厌氧过程。工业上也可通过上述乙烯水合法制备。比较两种方法的原料、速率和纯度是常见的考题切入点。
The most important chemical property of alcohols is oxidation. Primary alcohols like ethanol are oxidised to carboxylic acids by heating with acidified potassium dichromate(VI), which turns from orange to green. With ethanol:
醇最重要的化学性质是氧化。像乙醇这类伯醇，用酸性重铬酸钾(VI)加热氧化，生成相应的羧酸，重铬酸钾由橙色变为绿色。以乙醇为例：
C₂H₅OH + 2[O] → CH
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