📚 Organic Chemistry Fundamentals | 有机化学基础考点精讲
Organic chemistry is the branch of chemistry that focuses on the structure, properties, and reactions of carbon-containing compounds. Originally defined as the study of substances derived from living organisms, the field now encompasses synthetic materials such as plastics, pharmaceuticals, and dyes. A firm grasp of organic fundamentals is essential for understanding everything from biochemistry to industrial processes, and it underpins many of the core topics in IB and WJEC chemistry specifications.
有机化学是研究含碳化合物的结构、性质与反应的分支学科。早期它被定义为对来自生命体物质的探究，如今已涵盖塑料、药物和染料等合成材料。牢固掌握有机化学基础对于理解生物化学乃至工业过程至关重要，也是 IB 和 WJEC 化学课程中众多核心主题的根基。
1. Carbon: The Backbone of Organic Molecules | 碳：有机分子的骨架
Carbon’s unique position in organic chemistry arises from its electron configuration (1s² 2s² 2p²), which allows it to form four strong covalent bonds. This tetravalency enables the construction of diverse skeletons — chains, branched structures, and rings — via carbon–carbon bonds. The ability to catenate (form chains with other carbon atoms) far exceeds that of any other element, giving rise to millions of known organic compounds.
碳在有机化学中的独特地位源于其电子排布（1s² 2s² 2p²），使其能形成四个强共价键。这种四价特性通过碳-碳键得以构建多样的骨架——直链、支链和环状结构。碳的成链能力远胜于其他元素，从而催生了数以百万计的已知有机化合物。
Organic compounds may also contain single, double, or triple bonds between carbon atoms, influencing geometry and reactivity. The bonding context — sp³, sp², or sp hybridisation — determines molecular shape, bond angles, and the type of reactions a molecule can undergo.
有机化合物中的碳原子之间可形成单键、双键或三键，从而影响分子的几何构型与反应活性。键合环境（sp³、sp² 或 sp 杂化）决定了分子形状、键角以及所能发生的反应类型。
2. Hydrocarbons and Their Classification | 烃及其分类
Hydrocarbons are compounds composed solely of carbon and hydrogen. They are divided into aliphatic (alkanes, alkenes, alkynes, and cycloalkanes) and aromatic (containing benzene rings) families. Alkanes are saturated, containing only single C–C bonds, while alkenes and alkynes are unsaturated due to the presence of C=C and C≡C bonds, respectively.
烃是仅由碳和氢组成的化合物，可分为脂肪烃（烷烃、烯烃、炔烃、环烷烃）和芳香烃（含苯环）两大类。烷烃是饱和烃，只有 C–C 单键；而烯烃和炔烃则因含有 C=C 双键和 C≡C 三键而属于不饱和烃。
Alkanes have the general formula CₙH₂ₙ₊₂, while acyclic alkenes follow CₙH₂ₙ and alkynes CₙH₂ₙ₋₂. Aromatic hydrocarbons, such as benzene (C₆H₆), possess a delocalised π-electron system that confers exceptional stability.
烷烃的通式为 CₙH₂ₙ₊₂，无环烯烃的通式为 CₙH₂ₙ，炔烃为 CₙH₂ₙ₋₂。芳香烃如苯（C₆H₆）具有离域 π 电子体系，赋予其额外的稳定性。
3. Functional Groups: The Reactive Heart of Molecules | 官能团：分子的反应核心
A functional group is an atom or group of atoms within a molecule that is responsible for its characteristic chemical reactions. Molecules with the same functional group react in similar ways, regardless of the size of their carbon skeleton. Recognising functional groups is the first step in predicting organic reactivity.
官能团是分子中决定其特征化学反应的原子或原子团。具有相同官能团的分子，无论碳骨架大小如何，均表现出相似的化学行为。识别官能团是预测有机反应活性的第一步。
| Homologous Series | Functional Group | Prefix/Suffix |
|---|---|---|
| Alkane | (none, C–C) | -ane |
| Alkene | C=C | -ene |
| Alcohol | –OH (hydroxyl) | -ol |
| Aldehyde | –CHO (carbonyl at end) | -al |
| Ketone | –CO– (carbonyl within chain) | -one |
| Carboxylic acid | –COOH (carboxyl) | -oic acid |
| Ester | –COOR | -yl -oate |
| Amine | –NH₂ (amino) | -amine |
The table lists the most common functional groups examined at IB and WJEC level. Note that the same functional group appears in different classes of compounds but governs the same typical reactions.
上表列出了 IB 和 WJEC 考试中最常见的官能团。请注意，不同类别的化合物可能带有相同的官能团，而该官能团主导着相同的典型反应。
4. Homologous Series: Patterns in Properties | 同系列：性质的规律
A homologous series is a family of organic compounds with the same functional group, where successive members differ by a –CH₂– unit. Members of a series can be represented by a general molecular formula and exhibit gradual trends in physical properties, such as increasing melting and boiling points with rising molar mass due to stronger van der Waals forces.
同系列是一组具有相同官能团、相邻成员相差一个 –CH₂– 单元的有机化合物家族。同系列中各成员可用一个通式表示，并且物理性质呈现渐变趋势，例如随着摩尔质量增大，范德华力增强，熔点和沸点逐步升高。
Chemically, all members of a homologous series show the same characteristic reactions because they contain the same functional group. For instance, all alcohols undergo oxidation (when possible) and all alkenes undergo electrophilic addition.
由于含有相同的官能团，同系列中的所有成员在化学上表现出相同特征反应。例如，所有醇都能发生氧化反应（若可行），而所有烯烃都能发生亲电加成反应。
5. IUPAC Nomenclature: Systematic Naming | IUPAC 命名法：系统命名
The IUPAC system provides an unambiguous name for every organic molecule. The basic steps are: identify the longest continuous carbon chain containing the principal functional group, number the chain to give the functional group the lowest possible locant, name and number substituents, and assemble the name using prefixes and a suffix that indicates the highest-priority functional group.
IUPAC 系统为每个有机分子提供了唯一确定的名称。基本步骤为：找出含有主官能团的最长连续碳链；从最靠近官能团的一端给主链编号，使官能团编号最小；命名并标出取代基位置；最后用前缀和后缀组装名称，后缀表示优先级最高的官能团。
For example, the compound with a five-carbon chain, an –OH group on carbon 2, and a methyl group on carbon 3 is named 3-methylpentan-2-ol. Alkenes use the suffix ‘-ene’ with a number indicating the position of the double bond, such as but-2-ene.
例如，一个五碳链、在 2 号碳上带有 –OH 基团、3 号碳上带有一个甲基的化合物命名为 3-甲基-2-戊醇。烯烃使用后缀“-烯”，并用数字标明双键位置，如 2-丁烯。
6. Structural Isomerism: Same Formula, Different Connections | 结构异构：同分子式，不同连接
Structural isomers are compounds that share the same molecular formula but differ in the bonding arrangement of atoms. The three main types are chain isomerism (different carbon skeletons), position isomerism (functional group or substituent at different positions on the same skeleton), and functional group isomerism (different functional groups altogether, e.g., alcohols and ethers).
结构异构体是指分子式相同但原子连接方式不同的化合物。主要分为三种类型：碳链异构（碳骨架不同）、位置异构（官能团或取代基在相同骨架上位置不同）和官能团异构（官能团完全不同，如醇与醚）。
A classic example is C₄H₁₀, which exists as two chain isomers: butane and 2-methylpropane. The molecular formula C₃H₆O can represent a ketone (propanone) or an aldehyde (propanal), illustrating functional group isomerism.
经典实例为 C₄H₁₀，存在两种碳链异构体：丁烷和 2-甲基丙烷。分子式 C₃H₆O 既可以代表酮（丙酮）也可以代表醛（丙醛），展示了官能团异构。
7. Stereoisomerism: E/Z (Geometric) Isomers | 立体异构：E/Z (几何) 异构
Stereoisomers have the same structural formula but a different spatial arrangement of atoms. E/Z isomerism, also called geometric isomerism, occurs in alkenes (and cyclic compounds) where rotation about the double bond is restricted. For E/Z isomers to exist, each carbon of the C=C bond must carry two different groups.
立体异构体具有相同的结构式，但原子在空间排列不同。E/Z 异构，又称几何异构，出现在烯烃（及环状化合物）中，因双键无法自由旋转而产生。形成 E/Z 异构体的条件是，双键两个碳上的每个碳必须连有两个不同的基团。
Using the Cahn–Ingold–Prelog rules, each group on a double-bond carbon is assigned a priority based on atomic number. If the higher-priority groups are on the same side of the double bond, the isomer is Z (zusammen, together); if they are on opposite sides, it is E (entgegen, opposite). For simple cases, the older cis/trans terminology is still used, where cis corresponds to Z and trans to E.
根据 Cahn–Ingold–Prelog 规则，双键碳上的每个基团按照原子序数赋予优先级。若两个优先级较高的基团在双键的同侧，该异构体为 Z 构型；若在异侧，则为 E 构型。在简单情况下，仍使用顺反命名，顺式对应 Z 型，反式对应 E 型。
Consider but-2-ene: the cis isomer has both methyl groups on the same side, while the trans isomer has them on opposite sides. E/Z isomerism has important consequences for physical properties and biological activity.
以 2-丁烯为例，顺式异构体中两个甲基位于双键同侧，反式异构体则位于两侧。E/Z 异构对物理性质及生物活性具有重要影响。
8. Main Types of Organic Reactions | 有机反应的主要类型
Organic reactions are categorised by the overall transformation taking place. The key reaction types encountered in IB and WJEC syllabi include addition, substitution, elimination, oxidation, reduction, and polymerisation.
有机反应根据整体变换进行分类。IB 和 WJEC 课程中涉及的关键反应类型包括加成、取代、消除、氧化、还原和聚合。
- Addition: two reactants combine to form a single product; typical of unsaturated compounds (alkenes).
- 加成反应：两个反应物结合生成单一产物；常见于不饱和化合物（烯烃）。
- Substitution: one atom or group is replaced by another; common in alkanes (with halogens) and alcohols.
- 取代反应：一个原子或基团被另一个替代；常见于烷烃（与卤素）和醇。
- Elimination: a small molecule (e.g., H₂O, HX) is removed, forming an unsaturated product; alcohols undergo elimination to give alkenes.
- 消除反应：脱去一个小分子（如 H₂O、HX），生成不饱和产物；醇经消除反应生成烯烃。
- Oxidation / Reduction: gain of oxygen or loss of hydrogen (oxidation); loss of oxygen or gain of hydrogen (reduction). Alcohols oxidise to carbonyl compounds; aldehydes reduce to primary alcohols.
- 氧化/还原反应：得氧或失氢为氧化；失氧或得氢为还原。醇可氧化成羰基化合物；醛可还原为伯醇。
9. Alkanes: Combustion and Free-Radical Substitution | 烷烃：燃烧与自由基取代
Alkanes are relatively unreactive due to the strength of their C–C and C–H bonds, but they undergo two important types of reactions: combustion and halogenation.
由于 C–C 和 C–H 键较强，烷烃相对惰性，但仍能发生两类重要反应：燃烧与卤化。
Complete combustion in excess oxygen yields carbon dioxide and water, releasing large amounts of energy. Incomplete combustion produces carbon monoxide (a toxic gas) or soot (carbon particles). The balanced equation for the complete combustion of propane is:
在过量氧气中完全燃烧生成二氧化碳和水，并释放大量能量。不完全燃烧则生成有毒的一氧化碳或碳粒（黑烟）。丙烷完全燃烧的方程式为：
C₃H₈ + 5O₂ → 3CO₂ + 4H₂O
Halogenation of alkanes proceeds via a free-radical substitution mechanism that requires ultraviolet (UV) light to initiate. The reaction of methane with chlorine yields chloromethane and hydrogen chloride:
烷烃的卤化通过自由基取代机理进行，需紫外光引发。甲烷与氯气反应生成氯甲烷和氯化氢：
CH₄ + Cl₂ → CH₃Cl + HCl
The mechanism involves three stages: initiation (homolytic fission of halogen), propagation (chain-carrying steps giving products and new radicals), and termination (radicals combine).
该机理包含三个阶段：引发（卤素分子均裂）、增长（链传递步骤，生成产物与新自由基）和终止（自由基结合）。
10. Alkenes: Electrophilic Addition Reactions | 烯烃：亲电加成反应
The C=C double bond is an area of high electron density, making alkenes susceptible to attack by electrophiles (electron-pair acceptors). Electrophilic addition reactions are characteristic of alkenes and involve the addition of a reagent across the double bond, converting it into a single C–C bond.
C=C 双键区域具有高电子密度，使得烯烃易受亲电试剂（电子对受体）攻击。亲电加成反应是烯烃的特征反应，试剂跨越双键加成，将其转化为 C–C 单键。
Common addition reactions include:
常见加成反应包括：
- Hydrogenation: addition of H₂ with a nickel catalyst, converting alkenes to alkanes.
- 加氢：以镍为催化剂，加 H₂ 将烯烃转变为烷烃。
- Halogenation: addition of Br₂ or Cl₂; bromine water decolourises from orange to colourless, a test for unsaturation.
- 卤化：与 Br₂ 或 Cl₂ 加成；溴水由橙色变为无色，可作为不饱和键的检验方法。
- Hydrohalogenation: addition of HX (e.g., HBr). Unsymmetrical alkenes follow Markovnikov’s rule: the hydrogen atom attaches to the carbon with more hydrogen atoms already attached.
- 加卤化氢：与 HX（如 HBr）加成。不对称烯烃遵循马氏规则：氢原子加在原本氢较多的双键碳上。
- Hydration: addition of steam (H₂O) with an acid catalyst (H₃PO₄) to form alcohols, also Markovnikov-selective.
- 水合：以酸（磷酸）为催化剂，加蒸气（H₂O）生成醇，同样遵循马氏规则选择性。
The mechanism for addition of HBr to ethene is often illustrated with two steps: the electrophile H⁺ attacks the double bond, forming a carbocation intermediate, which then quickly combines with the bromide ion Br⁻.
溴化氢与乙烯加成的机理常用两步表示：亲电试剂 H⁺ 进攻双键形成碳正离子中间体，随后碳正离子迅速与溴离子 Br⁻ 结合。
11. Alcohols: Oxidation and Nucleophilic Substitution | 醇：氧化与亲核取代
The hydroxyl group makes alcohols versatile intermediates. Their two key reaction classes are oxidation (for primary and secondary alcohols) and nucleophilic substitution (where the –OH group is replaced by a halogen).
羟基使醇成为多功能中间体。其两类关键反应为氧化（适用于伯醇和仲醇）和亲核取代（–OH 被卤素替代）。
Oxidation uses acidified potassium dichromate(VI) as a common oxidising agent, which changes colour from orange (Cr₂O₇²⁻) to green (Cr³⁺). Primary alcohols are first oxidised to aldehydes, which can be further oxidised to carboxylic acids. To isolate the aldehyde, distillation is used; reflux yields the carboxylic acid. Secondary alcohols oxidise to ketones, which resist further oxidation. Tertiary alcohols do not oxidise under these conditions.
氧化反应常用酸化重铬酸钾(VI)作氧化剂，颜色由橙色（Cr₂O₇²⁻）变为绿色（Cr³⁺）。伯醇先氧化为醛，醛可继续氧化为羧酸。为分离出醛，可采用蒸馏；若采用回流则直接得到羧酸。仲醇氧化生成酮，酮不易继续被氧化。叔醇在此条件下不被氧化。
In substitution reactions, alcohols react with hydrogen halides (e.g., HBr) or other halogenating agents like PCl₅ or SOCl₂ to form haloalkanes. The hydroxyl group is protonated and then displaced by a halide ion, often via an S_N1 or S_N2 mechanism.
在取代反应中，醇与氢卤酸（如 HBr）或其他卤化试剂（如 PCl₅、SOCl₂）反应生成卤代烷。羟基先被质子化，然后被卤离子取代，常按 S_N1 或 S_N2 机理进行。
12. Carboxylic Acids and Esterification | 羧酸与酯化反应
Carboxylic acids contain the –COOH group. They are weak acids that partially dissociate in water to give H⁺ ions and carboxylate ions. They react with metals, bases, and carbonates, producing salts, water, and carbon dioxide as expected of an acid.
羧酸含有 –COOH 基团，是弱酸，在水中部分电离生成 H⁺ 和羧酸根离子。它们与金属、碱和碳酸盐发生典型的酸反应，生成盐、水和二氧化碳。
Esters are formed by the reaction of a carboxylic acid with an alcohol in the presence of a concentrated acid catalyst (usually H₂SO₄) and heat. This reversible condensation reaction is called esterification, typified by the general equation:
酯由羧酸与醇在浓酸催化剂（通常为浓硫酸）和加热条件下反应生成。这一可逆缩合反应称为酯化反应，通式如下：
RCOOH + R’OH ⇌ RCOOR’ + H₂O
Esters have characteristic fruity smells and are used as solvents, plasticisers, and flavourings. Naming an ester requires identifying the alcohol part as the alkyl group (e.g., ethyl) and the acid part as the carboxylate (e.g., ethanoate), giving names like ethyl ethanoate.
酯具有特有的水果香味，常被用作溶剂、增塑剂和调味剂。命名酯时，醇的部分作为烷基（如乙基），酸的部分转变为羧酸根（如乙酸根），从而得到如乙酸乙酯这样的名称。
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