📚 A-Level WJEC Chemistry: Core Organic Chemistry Revision Guide | A-Level WJEC 化学：有机化学基础 考点精讲
Organic chemistry forms a cornerstone of A-Level WJEC Chemistry. Mastering the fundamentals – functional groups, isomerism, reaction mechanisms, and synthetic pathways – is essential for success in both AS and A2 units. This revision guide breaks down every key concept into digestible, exam-focused sections.
有机化学是 WJEC A-Level 化学的基石。掌握官能团、异构现象、反应机理和合成路线等基础知识对于在 AS 和 A2 考试中取得成功至关重要。本考点精讲将每个关键概念分解为易于消化、紧扣考试的章节。
1. What is Organic Chemistry? | 有机化学简介
Organic chemistry is the study of carbon-containing compounds, with the exception of oxides, carbonates and hydrogencarbonates. Carbon’s ability to form four strong covalent bonds and catenate into chains and rings gives rise to millions of organic molecules.
有机化学是研究含碳化合物的学科，但不包括碳的氧化物、碳酸盐和碳酸氢盐。碳原子能够形成四个强共价键并通过自相连结成链和环，从而产生了数百万种有机分子。
In WJEC, you will encounter displayed, structural and skeletal formulae. A skeletal formula shows carbon-carbon bonds as lines, with carbon atoms at each vertex; hydrogen atoms are not drawn unless bonded to a heteroatom.
在 WJEC 考试中，你会遇到显示式、结构简式和骨架式。骨架式将碳-碳键显示为折线，每个顶点代表一个碳原子；氢原子除非与杂原子相连，否则不画出来。
2. Functional Groups & Homologous Series | 官能团与同系列
A functional group is an atom or group of atoms that gives a compound its characteristic chemical properties. A homologous series is a family of compounds with the same functional group, each member differing by a –CH₂– unit.
官能团是赋予化合物特征化学性质的原子或原子团。同系列是具有相同官能团的一组化合物，相邻成员之间相差一个 –CH₂– 单元。
Key WJEC functional groups: alkanes (C–C, C–H only), alkenes (C=C), halogenoalkanes (R–X), alcohols (–OH), aldehydes (–CHO), ketones (C–CO–C), carboxylic acids (–COOH) and amines (–NH₂). Each series follows a general formula, e.g. alkanes: CₙH₂ₙ₊₂, alkenes: CₙH₂ₙ.
WJEC 重点官能团：烷烃（只含 C–C 和 C–H）、烯烃 (C=C)、卤代烷 (R–X)、醇 (–OH)、醛 (–CHO)、酮 (C–CO–C)、羧酸 (–COOH) 和胺 (–NH₂)。每个同系列都有通式，例如烷烃：CₙH₂ₙ₊₂，烯烃：CₙH₂ₙ。
3. IUPAC Naming Rules | IUPAC命名规则
IUPAC names are built from: prefix(es) – parent chain – suffix. The parent chain is the longest continuous carbon chain containing the principal functional group. Numbering gives the lowest possible locants to the functional group and substituents.
IUPAC 命名由三部分构成：前缀 – 母链 – 后缀。母链是包含主官能团的最长连续碳链。编号时应使官能团和取代基获得最小的定位号。
If more than one identical substituent exists, use di-, tri-, tetra-. Substituents are listed alphabetically. For alkenes, the position of the double bond is indicated before the suffix ‘-ene’, e.g. but-1-ene, but-2-ene.
如果存在多个相同取代基，则使用二、三、四等前缀。取代基按字母顺序排列。对于烯烃，双键的位置标在后缀“-烯”之前，例如丁-1-烯、丁-2-烯。
4. Structural Isomerism | 构造异构
Structural isomers have the same molecular formula but different structural arrangements of atoms. Chain isomers differ in the carbon skeleton; position isomers differ in the location of a functional group; functional group isomers differ in the functional group itself.
构造异构体具有相同的分子式，但原子的连接方式不同。碳链异构体碳骨架不同；位置异构体官能团位置不同；官能团异构体所含官能团不同。
For example, C₃H₆O can represent propanal (an aldehyde), propanone (a ketone) or prop-2-en-1-ol (an unsaturated alcohol). Recognizing these possibilities is vital for structure determination questions.
例如，分子式 C₃H₆O 可以表示丙醛（一种醛）、丙酮（一种酮）或丙烯醇（一种不饱和醇）。在结构推断题中识别这些可能性至关重要。
5. Stereoisomerism | 立体异构
Stereoisomers have the same structural formula but a different spatial arrangement. E/Z isomerism occurs in alkenes with restricted rotation around the C=C bond. Each doubly bonded carbon must have two different groups attached. The CIP priority rules (based on atomic number) assign E (opposite sides) or Z (same side) configurations.
立体异构体构造式相同但空间排列不同。E/Z 异构发生在因双键不能自由旋转的烯烃中，每个双键碳必须连有两个不同的基团。根据 CIP 顺序规则（基于原子序数），将构型规定为 E（异侧）或 Z（同侧）。
Optical isomerism arises in molecules containing a chiral centre – a carbon atom bonded to four different groups. The two non-superimposable mirror images are called enantiomers and rotate plane-polarised light in opposite directions.
光学异构存在于含有手性中心的分子中，即连接四个不同基团的碳原子。两种不能重叠的镜像称为对映异构体，它们使平面偏振光向相反方向旋转。
6. Alkanes & Free-Radical Substitution | 烷烃与自由基取代
Alkanes are relatively unreactive due to strong C–C and C–H bonds, but they undergo combustion and radical substitution. Complete combustion produces CO₂ and H₂O; incomplete combustion can produce CO and soot.
由于 C–C 和 C–H 键很强，烷烃相对不活泼，但能发生燃烧和自由基取代反应。完全燃烧生成 CO₂ 和 H₂O；不完全燃烧可能产生 CO 和碳粒。
Chlorination of methane proceeds via a free-radical mechanism: initiation – Cl₂ undergoes homolytic fission to form Cl•; propagation – Cl• abstracts H from CH₄, then •CH₃ reacts with Cl₂; termination – two radicals combine. UV light is required.
Initiation: Cl₂ → 2Cl• (UV light)
甲烷的氯化反应通过自由基机理进行：引发 – Cl₂ 均裂生成 Cl•；链增长 – Cl• 夺取 CH₄ 的 H，随后 •CH₃ 与 Cl₂ 反应；终止 – 两个自由基结合。反应需要紫外光。
Propagation: Cl• + CH₄ → •CH₃ + HCl; •CH₃ + Cl₂ → CH₃Cl + Cl•
7. Alkenes & Electrophilic Addition | 烯烃与亲电加成
The C=C double bond is an electron-rich region, making alkenes susceptible to electrophilic attack. Addition of HBr, Br₂, H₂SO₄ and H₂O (via H⁺ catalysis) proceeds via a carbocation intermediate.
C=C 双键是一个富电子区域，使烯烃容易受到亲电试剂进攻。HBr、Br₂、H₂SO₄ 以及 H₂O（H⁺催化）的加成反应均经由碳正离子中间体进行。
With unsymmetrical alkenes, Markovnikov’s rule applies: the hydrogen atom attaches to the carbon with more hydrogen atoms already, because the more stable carbocation is formed. For example, propene + HBr gives mainly 2-bromopropane, not 1-bromopropane.
对于不对称烯烃，适用马氏规则：氢原子加到含氢较多的双键碳上，因为这样会形成更稳定的碳正离子。例如，丙烯与 HBr 主要生成 2-溴丙烷，而非 1-溴丙烷。
8. Haloalkanes: Nucleophilic Substitution & Elimination | 卤代烷：亲核取代与消去
Haloalkanes contain a polar C–X bond; the carbon is electron-deficient and can be attacked by nucleophiles such as OH⁻, CN⁻ and NH₃. The halogen acts as a leaving group. Hydrolysis with aqueous NaOH yields an alcohol.
卤代烷含有极性 C–X 键；碳原子缺电子，可被 OH⁻、CN⁻ 和 NH₃ 等亲核试剂进攻。卤原子作为离去基团。用 NaOH 水溶液水解生成醇。
Nucleophilic substitution follows either an SN1 or SN2 pathway depending on the class of haloalkane. Tertiary haloalkanes favour SN1 via a stable carbocation; primary haloalkanes undergo SN2 in one step with inversion of configuration.
亲核取代按卤代烷的级别遵循 SN1 或 SN2 途径。叔卤代烷倾向通过稳定的碳正离子走 SN1 路径；伯卤代烷则通过 SN2 一步完成且伴随构型翻转。
When heated with KOH in ethanol, haloalkanes undergo elimination to form alkenes. The reagent acts as a base, removing a β-hydrogen and the halide ion simultaneously.
与 KOH 的乙醇溶液共热时，卤代烷发生消去反应生成烯烃。此时试剂起到碱的作用，同时拔除 β-氢和卤离子。
9. Alcohols: Oxidation & Dehydration | 醇：氧化与脱水
Primary alcohols can be oxidised to aldehydes and then to carboxylic acids; secondary alcohols oxidise to ketones; tertiary alcohols resist oxidation. Acidified potassium dichromate(VI) (K₂Cr₂O₇/H⁺) is the usual oxidising agent, turning from orange to green.
伯醇可被氧化成醛，进而氧化成羧酸；仲醇氧化成酮；叔醇不易被氧化。常用的氧化剂是酸化重铬酸钾 (K₂Cr₂O₇/H⁺)，颜色由橙变绿。
To stop at the aldehyde stage, the aldehyde must be distilled off immediately; for the acid, heat under reflux with excess oxidising agent. For secondary alcohols, reflux produces the ketone.
为得到醛阶段，必须立即将醛蒸馏出来；若要得到酸，则加过量氧化剂并回流。仲醇回流即可得到酮。
Alcohols can be dehydrated to alkenes by heating with concentrated H₂SO₄ or passing over hot Al₂O₃. This is an elimination reaction; primary alcohols give terminal alkenes.
醇可通过与浓硫酸共热或通过热氧化铝催化剂脱水生成烯烃。这是一个消去反应；伯醇生成端基烯烃。
10. Reaction Pathways in Organic Synthesis | 有机合成路线
WJEC questions often require you to propose synthetic routes linking different functional groups. For instance: alkane → haloalkane (radical substitution), haloalkane → alcohol (nucleophilic substitution), alcohol → aldehyde → carboxylic acid (oxidation), alcohol → alkene (elimination), alkene → haloalkane (electrophilic addition).
WJEC 常要求设计连接不同官能团的合成路线。例如：烷烃 → 卤代烷（自由基取代），卤代烷 → 醇（亲核取代），醇 → 醛 → 羧酸（氧化），醇 → 烯烃（消去），烯烃 → 卤代烷（亲电加成）。
When planning a synthesis, you must consider reagents, conditions and the risk of unwanted side reactions. Using a reaction map helps you visualise how to convert one functional group into another in a logical sequence.
设计合成时，必须考虑试剂、条件以及不希望发生的副反应。利用反应关系图有助于你直观地按逻辑顺序将一种官能团转化为另一种官能团。
11. Types of Bond Fission & Curly Arrows | 键断裂类型与弯箭头
Bond breaking can be homolytic (each atom takes one electron, forming two radicals) or heterolytic (both electrons go to one atom, forming a cation and an anion). Homolytic fission is shown using a single barbed arrow (fish-hook), while heterolytic fission uses a full curly arrow.
键的断裂可以是均裂（每个原子各得一个电子，形成两个自由基）或异裂（两个电子归一个原子，形成阳离子和阴离子）。均裂用单钩箭头表示，异裂用全弯箭头表示。
In organic mechanisms, curly arrows represent the movement of an electron pair. They must start from a lone pair or a bond and point precisely towards an atom or between two atoms. Accurate arrow drawing is a common mark-earning skill in WJEC exams.
在有机机理中，弯箭头表示电子对的移动。箭头必须从孤对电子或一根键出发，精确指向某个原子或两个原子之间。正确绘制箭头是 WJEC 考试中常见的得分点。
12. Exam Focus & Common Pitfalls | 考试聚焦与常见错误
Be precise in naming: always select the longest chain containing the highest-priority functional group. Omit spaces in IUPAC names and use hyphens between numbers and words. Do not confuse skeletal formulae with structural formulae.
命名时务必精确：始终选择包含最优先官能团的最长链。IUPAC 名称中不留空格，数字与文字之间用连字符。不要把骨架式误当成结构简式。
When drawing optical isomers, clearly show the 3D tetrahedral arrangement using wedged and dashed bonds. For E/Z isomers, assign priority carefully; never assume trans = E and cis = Z without applying the CIP rules.
绘制光学异构体时，要用楔形键和虚线键清晰表现三维四面体排列。对于 E/Z 异构，仔细确定优先顺序；不应用 CIP 规则就简单认为 trans 即 E、cis 即 Z。
In mechanism questions, show all relevant charges, lone pairs and curly arrows. If asked for a reaction pathway, include reagents and essential conditions. Practise multi-step synthesis with unfamiliar starting materials; this sharpens problem-solving for the synoptic paper.
在机理题中，要标出所有相关电荷、孤对电子和弯箭头。如果被要求写出反应路线，需注明试剂和关键条件。多练习陌生原料的多步合成；这能提高你在综测试卷中的解题能力。
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