📚 1 Fundamentals of organic chemistry | 有机化学基础
Organic chemistry is the branch of chemistry that deals with the structure, properties, composition, reactions and preparation of carbon-containing compounds. Unlike inorganic compounds, the vast diversity of organic molecules stems from carbon's unique ability to form stable covalent bonds with itself and other elements such as hydrogen, oxygen, nitrogen, sulfur and the halogens. Understanding the fundamentals is essential for mastering topics like biochemistry, medicinal chemistry and materials science.
有机化学是研究含碳化合物的结构、性质、组成、反应和制备的化学分支。与无机物不同，有机分子的巨大多样性源于碳独特的成键能力——它能与自身以及氢、氧、氮、硫和卤素等元素形成稳定的共价键。掌握这些基础知识对深入学习生物化学、药物化学和材料科学至关重要。
1. The Nature of Organic Chemistry | 有机化学的本质
Historically, organic compounds were believed to originate only from living organisms through a 'vital force'. This idea was disproved in 1828 when Friedrich Wöhler synthesised urea, an organic compound, from the inorganic salt ammonium cyanate. Today, organic chemistry is defined as the study of carbon compounds, with a few exceptions: oxides of carbon (CO, CO₂), carbonates (CO₃²⁻), cyanides (CN⁻) and carbides are typically considered inorganic. Carbon's versatility arises from its electron configuration (1s² 2s² 2p²), allowing it to form four covalent bonds, often resulting in chains, rings and multiple bonds.
历史上，人们曾认为有机化合物只能通过“生命力”从生物体内产生。这一观念在1828年被打破，弗里德里希·维勒用无机盐氰酸铵合成了有机化合物尿素。如今，有机化学被定义为研究碳化合物的学科，但有一些例外：碳的氧化物（CO、CO₂）、碳酸盐（CO₃²⁻）、氰化物（CN⁻）和碳化物通常被视为无机物。碳的多功能性源于其电子排布（1s² 2s² 2p²），可形成四个共价键，从而构建出链状、环状和多重键结构。
2. Homologous Series | 同系列
A homologous series is a family of organic compounds that share the same general formula, functional group and similar chemical properties. Within a series, each successive member differs from the previous one by a –CH₂– unit. As the carbon chain length increases, physical properties such as boiling point and viscosity show a gradual trend, while chemical reactivity remains largely constant. Common examples include the alkanes (CₙH₂ₙ₊₂), alkenes (CₙH₂ₙ) and alcohols (CₙH₂ₙ₊₁OH).
同系列是一类具有相同通式、相同官能团和相似化学性质的有机化合物家族。在同系列中，每相邻两个成员相差一个 –CH₂– 单元。随着碳链增长，物理性质如沸点和黏度呈现渐变趋势，而化学性质基本保持不变。常见的同系列包括烷烃（CₙH₂ₙ₊₂）、烯烃（CₙH₂ₙ）和醇（CₙH₂ₙ₊₁OH）。
| Homologous Series | 同系列 | General Formula | 通式 | Functional Group | 官能团 |
|---|---|---|
| Alkanes | 烷烃 | CₙH₂ₙ₊₂ | None (C–C, C–H only) |
| Alkenes | 烯烃 | CₙH₂ₙ | C=C |
| Alkynes | 炔烃 | CₙH₂ₙ₋₂ | C≡C |
| Alcohols | 醇 | CₙH₂ₙ₊₁OH | –OH (hydroxyl) |
3. Functional Groups | 官能团
A functional group is an atom or a group of atoms within a molecule that is responsible for its characteristic chemical reactions. Compounds with the same functional group undergo similar reactions, which allows chemists to predict the behaviour of unfamiliar molecules. The table below lists the most common functional groups encountered in IB Chemistry alongside their structural representations and naming suffixes.
官能团是分子中负责其特征化学反应的原子或原子团。具有相同官能团的化合物会发生相似的反应，这使得化学家能够预测陌生分子的行为。下表列出了IB化学中最常见的官能团、其结构表示和命名后缀。
| Functional Group | 官能团 | Structure | 结构 | Suffix/Prefix | 后缀/前缀 |
|---|---|---|
| Alkane | 烷烃 | C–C | -ane |
| Alkene | 烯烃 | C=C | -ene |
| Halogenoalkane | 卤代烷 | –X (F, Cl, Br, I) | halo- (prefix) |
| Alcohol | 醇 | –OH | -ol |
| Aldehyde | 醛 | –CHO | -al |
| Ketone | 酮 | >C=O | -one |
| Carboxylic acid | 羧酸 | –COOH | -oic acid |
| Ester | 酯 | –COO– | -oate |
| Amine | 胺 | –NH₂ | -amine |
| Amide | 酰胺 | –CONH₂ | -amide |
| Nitrile | 腈 | –C≡N | -nitrile |
4. Representing Organic Molecules – Types of Formulas | 表示有机分子 – 分子式种类
Organic molecules can be represented in several ways, each providing different levels of structural detail. The empirical formula gives the simplest whole-number ratio of atoms; the molecular formula shows the actual number of atoms of each element. A full structural formula (displayed formula) shows every bond and atom, while a condensed structural formula omits some bonds for simplicity. The skeletal formula uses lines to represent carbon-carbon bonds, with carbon atoms assumed at vertices and hydrogen atoms omitted unless part of a functional group.
有机分子可以用多种方式表示，不同方式提供的结构细节层次不同。实验式给出原子最简整数比；分子式显示每种元素的实际原子数目。完全结构式（显示式）展示全部化学键和原子，而简写结构式为了简便省略部分化学键。骨架式用线条表示碳-碳键，顶点处假定为碳原子，除非属于官能团的一部分，否则氢原子被省略。
For example, propan-1-ol can be represented as:
例如，1-丙醇可以表示为：
- Empirical formula | 实验式: C₃H₈O
- Molecular formula | 分子式: C₃H₈O
- Full structural formula | 完全结构式: H–C–C–C–O–H (with all hydrogens shown)
- Condensed formula | 简写结构式: CH₃CH₂CH₂OH
- Skeletal formula | 骨架式: A zigzag line of three vertices ending with –OH
5. IUPAC Naming System | IUPAC 命名系统
The International Union of Pure and Applied Chemistry (IUPAC) system provides a systematic way to name organic compounds. The name consists of a prefix (for substituents), a stem (indicating the number of carbons in the longest chain) and a suffix (for the principal functional group). Numbering of the carbon chain must give the lowest possible numbers to the substituents and functional groups. When multiple identical substituents are present, prefixes such as di-, tri- and tetra- are used, and their positions are separated by commas. Substituents are listed in alphabetical order.
国际纯粹与应用化学联合会（IUPAC）系统为有机化合物命名提供了系统的方法。名称由前缀（取代基）、母体（最长碳链的碳原子数）和后缀（主要官能团）组成。碳链的编号必须使取代基和官能团的位置编号尽可能小。当存在多个相同的取代基时，使用二、三、四等前缀，位置编号之间用逗号隔开。取代基按字母顺序排列。
Example | 示例: CH₃CH(CH₃)CH₂CH₃ is named 2-methylbutane. The longest chain has four carbons (butane), and a methyl group is attached to carbon-2.
CH₃CH(CH₃)CH₂CH₃ 的名称为 2-甲基丁烷。最长碳链有四个碳（丁烷），一个甲基连接在 2 号碳上。
Another example | 另一个示例: CH₃CH(Cl)CH₂COOH is named 3-chlorobutanoic acid, where numbering starts from the carboxylic acid carbon.
CH₃CH(Cl)CH₂COOH 命名为 3-氯丁酸，编号从羧基碳开始。
6. Saturated, Unsaturated, Aliphatic and Aromatic | 饱和、不饱和、脂肪族和芳香族
Organic compounds can be classified based on their bonding and structure. Saturated compounds contain only single bonds (e.g., alkanes), whereas unsaturated compounds possess at least one double or triple bond (e.g., alkenes, alkynes). Aliphatic compounds consist of straight or branched chains and non-aromatic rings, while aromatic compounds contain one or more benzene rings or exhibit delocalised pi electrons that confer extra stability. This distinction is important because aromatic compounds undergo substitution rather than addition reactions under standard conditions.
有机化合物可以根据其成键和结构进行分类。饱和化合物仅含单键（例如烷烃），而不饱和化合物至少含有一个双键或三键（例如烯烃、炔烃）。脂肪族化合物由直链、支链或非芳香环组成，而芳香族化合物含有一个或多个苯环，或者含有离域π电子从而具有额外稳定性。这一区分非常重要，因为在标准条件下，芳香族化合物倾向于发生取代反应而非加成反应。
7. Classification of Carbon Atoms and Compounds | 碳原子和化合物的分类
Carbon atoms in organic molecules are classified as primary (1°), secondary (2°), tertiary (3°) or quaternary (4°) based on how many other carbon atoms they are attached to. A primary carbon is bonded to one other carbon, a secondary to two, a tertiary to three, and a quaternary to four. This classification is applied to halogenoalkanes and alcohols to describe the type of compound: a primary alcohol has the –OH group attached to a 1° carbon, a secondary alcohol to a 2° carbon, and a tertiary alcohol to a 3° carbon.
有机分子中的碳原子根据其所连接的其他碳原子数目可分为伯碳（1°）、仲碳（2°）、叔碳（3°）或季碳（4°）。伯碳连有1个其他碳原子，仲碳连有2个，叔碳连有3个，季碳连有4个。这一分类适用于卤代烷和醇，用以描述化合物类型：伯醇的 –OH 连在伯碳上，仲醇连在仲碳上，叔醇连在叔碳上。
For instance, propan-1-ol (CH₃CH₂CH₂OH) is a primary alcohol; propan-2-ol ((CH₃)₂CHOH) is a secondary alcohol; 2-methylpropan-2-ol ((CH₃)₃COH) is a tertiary alcohol.
例如，1-丙醇（CH₃CH₂CH₂OH）是伯醇；2-丙醇（(CH₃)₂CHOH）是仲醇；2-甲基-2-丙醇（(CH₃)₃COH）是叔醇。
8. Structural Isomerism | 结构异构
Structural isomers possess the same molecular formula but differ in the arrangement of atoms, leading to different physical and chemical properties. There are three main types: chain isomerism (different arrangement of the carbon skeleton, e.g., straight-chain vs. branched), position isomerism (the functional group is attached to a different carbon atom) and functional group isomerism (different functional groups altogether, such as alcohols and ethers, or aldehydes and ketones). Recognising isomers is crucial for understanding reaction outcomes and properties.
结构异构体具有相同的分子式，但原子排列方式不同，从而导致不同的物理和化学性质。结构异构主要分为三种类型：碳链异构（碳骨架排列不同，如直链与支链）、位置异构（官能团连接在不同的碳原子上）和官能团异构（官能团完全不同，如醇与醚，或醛与酮）。识别异构体对于理解反应产物和物质性质至关重要。
Example: the molecular formula C₄H₁₀ can represent butane (CH₃CH₂CH₂CH₃) and methylpropane (CH₃CH(CH₃)CH₃) – chain isomers. The formula C₃H₈O corresponds to propan-1-ol, propan-2-ol (position isomers) and methoxyethane (CH₃OCH₂CH₃) as a functional group isomer.
示例：分子式 C₄H₁₀ 可表示丁烷（CH₃CH₂CH₂CH₃）和 2-甲基丙烷（CH₃CH(CH₃)CH₃）——链异构体。分子式 C₃H₈O 可对应 1-丙醇、2-丙醇（位置异构体）和甲氧基乙烷（CH₃OCH₂CH₃）作为官能团异构体。
9. Common Types of Organic Reactions | 常见有机反应类型
Organic reactions are categorised based on the overall transformation occurring. Substitution reactions involve the replacement of one atom or group by another (e.g., halogenation of alkanes). Addition reactions are typical of unsaturated compounds, where atoms are added across a double or triple bond (e.g., bromination of ethene). Elimination reactions remove atoms or groups from a molecule to form a multiple bond (e.g., dehydration of alcohols to alkenes). Oxidation and reduction reactions are also widely used: primary alcohols can be oxidised to aldehydes and then to carboxylic acids, while aldehydes can be reduced back to primary alcohols. Condensation and hydrolysis reactions are important in polymer and biochemistry.
有机反应根据发生的整体转变进行分类。取代反应涉及一个原子或基团被另一个取代（例如烷烃的卤化）。加成反应是不饱和化合物的典型反应，原子加合到双键或三键之上（例如乙烯的溴化）。消除反应使分子失去原子或基团形成多重键（例如醇脱水生成烯烃）。氧化与还原反应也被广泛应用：伯醇可被氧化为醛，进而氧化为羧酸；醛则可被还原回伯醇。缩合与水解反应在聚合物和生物化学中尤为重要。
10. Introduction to Aromatic Compounds – Benzene | 芳香族化合物简介 – 苯
Benzene (C₆H₆) is the parent aromatic hydrocarbon. Its structure is often depicted with alternating single and double bonds as proposed by Kekulé, but in reality the six electrons in the pi system are delocalised above and below the plane of the ring, giving equal bond lengths and exceptional stability. This delocalisation energy means benzene resists addition reactions and instead undergoes electrophilic substitution, such as nitration and halogenation, in the presence of a catalyst. Benzene and its derivatives form the basis of a vast array of compounds including plastics, dyes and pharmaceuticals.
苯（C₆H₆）是母体芳香烃。其结构常以凯库勒式单双键交替的形式表示，但实际上六个π电子在环平面上下离域，所有碳-碳键长相等，具有特殊的稳定性。这种离域能使得苯不易发生加成反应，而是在催化剂存在下进行亲电取代反应，例如硝化和卤化。苯及其衍生物构成了塑料、染料和药物等大量化合物的基础。
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