📚 IB Chemistry: Fundamentals of Organic Chemistry Key Concepts | IB 化学：有机化学基础 考点精讲
Organic chemistry is the chemistry of carbon compounds. In IB Chemistry, grasping the fundamentals – from structural formulas and functional groups to nomenclature and isomerism – is essential for success. This article distils the core points of the SL and HL syllabus, pairing clear explanations with bilingual key notes to help you master the basics and build confidence for Paper 1, Paper 2 and the internal assessment.
有机化学是碳化合物的化学。在 IB 化学中，从结构式、官能团到命名和异构现象，掌握这些基础是取得好成绩的关键。本文浓缩了 SL 与 HL 课程的核心考点，用清晰的中英双语讲解帮助你扎实基本功，为卷一、卷二以及内部评估打下自信的基础。
1. What Defines an Organic Compound? | 什么是有机化合物？
An organic compound is a carbon-containing compound, with a few traditional exceptions such as carbon oxides, carbonates, hydrogencarbonates and cyanides. The key feature is a carbon skeleton, often bonded to hydrogen, oxygen, nitrogen, halogens and other atoms. Carbon’s ability to form four stable covalent bonds allows for chain, branched and cyclic structures.
有机化合物是含碳的化合物，少数传统例外如碳的氧化物、碳酸盐、碳酸氢盐和氰化物。其关键特征是碳骨架，通常与氢、氧、氮、卤素等原子成键。碳能够形成四个稳定的共价键，从而产生直链、支链和环状结构。
2. Homologous Series: The Backbone of Classification | 同系物：分类的骨架
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 by a –CH₂– unit. For example, alkanes have the general formula CₙH₂ₙ₊₂, while alkenes follow CₙH₂ₙ. Understanding homologous series allows you to predict reactivity and trends such as boiling points increasing with chain length.
同系物是一类具有相同通式、相似化学性质且物理性质呈渐变趋势的有机化合物家族。每个相继成员相差一个 –CH₂– 单元。例如，烷烃通式为 CₙH₂ₙ₊₂，而烯烃通式为 CₙH₂ₙ。掌握同系物有助于预测反应性以及沸点随碳链增长而升高的趋势。
3. Functional Groups: Chemistry’s Reactive Centres | 官能团：化学反应的活性中心
A functional group is an atom or group of atoms that gives a molecule its characteristic reactions. IB expects you to recall the functional groups for alkanes, alkenes, alkynes, halogenoalkanes, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines, amides, nitriles and arenes. The general representation R– is used for alkyl chains, while Ar– stands for aryl (aromatic) groups.
官能团是赋予分子特征反应的原子或原子团。IB 要求你牢记烷烃、烯烃、炔烃、卤代烷、醇、醚、醛、酮、羧酸、酯、胺、酰胺、腈和芳烃的官能团。通常用 R– 表示烷基链，Ar– 表示芳基。
| Homologous Series | Functional Group | Suffix/Prefix |
|---|---|---|
| Alkane | C–C (single bond) | -ane |
| Alkene | C=C | -ene |
| Alkyne | C≡C | -yne |
| Halogenoalkane | –X (F, Cl, Br, I) | fluoro-, chloro-, etc. |
| Alcohol | –OH | -ol |
| Aldehyde | –CHO | -al |
| Ketone | C–CO–C | -one |
| Carboxylic acid | –COOH | -oic acid |
| Ester | –COO– | -oate |
4. IUPAC Nomenclature: The Language of Organic Chemistry | IUPAC 命名法：有机化学的语言
IUPAC rules provide a systematic way to name any organic molecule. The core steps are: find the longest continuous carbon chain (parent chain); identify the principal functional group to determine the suffix; number the chain to give the principal group the lowest possible locant; name and number substituents as prefixes in alphabetical order. For alkenes and alkynes, the double or triple bond takes precedence in numbering over alkyl substituents.
IUPAC 规则提供了系统命名有机分子的方法。核心步骤为：找到最长的连续碳链（主链）；确定主官能团以选定后缀；为链编号，使主官能团具有最低可能的位置号；命名取代基，按字母顺序作为前缀。对于烯烃和炔烃，双键或三键在编号时优先于烷基取代基。
Practice example: CH₃–CH₂–CH(CH₃)–CH₂–CH₃ is 3-methylpentane, not 2-ethylbutane, because the longest chain is five carbons. For a compound bearing both an –OH and a C=C, the suffix -ol retains priority, e.g. but-3-en-2-ol.
练习示例：CH₃–CH₂–CH(CH₃)–CH₂–CH₃ 是 3-甲基戊烷，而非 2-乙基丁烷，因为最长的碳链是五个碳。对于一个同时带有 –OH 和 C=C 的化合物，后缀 -ol 保留优先权，例如丁-3-烯-2-醇。
5. Empirical, Molecular and Structural Formulas | 实验式、分子式与结构式
The empirical formula is the simplest whole-number ratio of atoms in a compound, while the molecular formula gives the actual number of each atom. For butane, C₄H₁₀ is the molecular formula, but the empirical formula is C₂H₅. Structural formulas can be displayed full (showing all bonds), condensed (e.g. CH₃CH₂CH₂OH), or skeletal (line-angle drawings where each vertex represents a carbon and hydrogens are implied). IB requires you to interpret and draw all three representations fluently.
实验式是化合物中各原子最简整数比，而分子式给出的是每种原子的实际数目。对于丁烷，C₄H₁₀ 是分子式，而实验式为 C₂H₅。结构式可以完整展开（显示所有化学键）、简写（如 CH₃CH₂CH₂OH）或骨架式（线角式，每个顶点代表一个碳原子，氢原子隐含）。IB 要求学生能熟练解读并画出所有三种表示法。
6. Isomerism: Same Formula, Different Worlds | 异构现象：相同分子式，不同世界
Isomers are compounds with the same molecular formula but different arrangements of atoms. Structural isomers differ in the connectivity of atoms: chain isomers (different carbon skeleton), position isomers (same functional group at different locations), and functional group isomers (different functional groups, e.g. propanal and propanone, both C₃H₆O). IB expects you to recognise and draw all types up to six carbon atoms and to explain that isomers often have distinct physical and chemical properties.
异构体是分子式相同但原子排列不同的化合物。结构异构体在原子连接方式上不同：碳链异构（碳骨架不同）、位置异构（同一官能团在不同位置）和官能团异构（不同官能团，例如丙醛和丙酮，均为 C₃H₆O）。IB 要求能识别并画出最多六个碳原子的所有类型，并解释异构体通常具有不同的物理和化学性质。
7. Stereoisomerism: E/Z and Optical Isomers (HL) | 立体异构：E/Z 异构与光学异构 (HL)
Stereoisomers have the same structural formula but different spatial arrangement of atoms. Two key types in IB HL are E/Z isomerism (geometric isomerism) and optical isomerism. E/Z isomers arise from restricted rotation around a C=C double bond or a ring, where each doubly bonded carbon carries two different groups. Use the Cahn–Ingold–Prelog priority rules: higher atomic number → higher priority. If the higher priority groups are on the same side, it is Z (zusammen); if opposite, E (entgegen). Optical isomers are non-superimposable mirror images (enantiomers) that contain a chiral carbon – a carbon with four different groups attached. Enantiomers rotate plane-polarised light equally but in opposite directions.
立体异构体具有相同的结构式，但原子的空间排列不同。IB HL 中的两种关键类型是 E/Z 异构（几何异构）和光学异构。E/Z 异构体源于 C=C 双键或环周围的旋转受限，每个双键碳上连接两个不同的基团。使用 Cahn–Ingold–Prelog 顺序规则：原子序数越高 → 优先级越高。如果较高优先级的基团在双键同侧，则为 Z (zusammen)；如果在对侧，则为 E (entgegen)。光学异构体是互为不可重合的镜像（对映体），其分子含有一个手性碳——即连接四个不同基团的碳原子。对映体对平面偏振光的旋转角度相等但方向相反。
Priority order: I > Br > Cl > S > F > O > N > C > H
8. Primary, Secondary and Tertiary Classification | 伯、仲、叔的分类
For halogenoalkanes and alcohols, classification depends on the carbon atom directly bonded to the functional group. A primary (1°) carbon is attached to only one other carbon, secondary (2°) to two, and tertiary (3°) to three. This directly affects the mechanism of nucleophilic substitution: 1° favours Sₙ2, while 3° favours Sₙ1. In amines, the classification counts the number of carbon atoms bonded to the nitrogen atom.
对于卤代烷和醇，分类取决于与官能团直接相连的碳原子。伯 (1°) 碳只与一个其他碳相连，仲 (2°) 与两个，叔 (3°) 与三个。这直接影响亲核取代机理：1° 倾向 Sₙ2，而 3° 倾向 Sₙ1。对于胺，分类计数与氮原子成键的碳原子数目。
9. Key Reaction Types: A Mind Map for Mechanism | 关键反应类型：机理思维导图
IB organic reactions can be grouped into addition, substitution, elimination, oxidation, reduction, condensation and hydrolysis. Alkenes undergo electrophilic addition; halogenoalkanes undergo nucleophilic substitution; alcohols can be oxidised (1° to aldehyde then carboxylic acid, 2° to ketone; 3° resists oxidation). Carboxylic acids and alcohols condense to esters. Mastering these patterns allows you to deduce products in unfamiliar reactions.
IB 有机反应可归纳为加成、取代、消除、氧化、还原、缩合和水解。烯烃发生亲电加成；卤代烷发生亲核取代；醇可被氧化（1° 醇氧化成醛再成羧酸，2° 醇氧化成酮；3° 醇不易被氧化）。羧酸与醇缩合生成酯。掌握这些模式使你能够在陌生反应中推断产物。
10. Fuels and Combustion: The Simplest Organic Reaction | 燃料与燃烧：最简单的有机反应
Alkanes and alcohols are common fuels. Complete combustion in excess oxygen produces CO₂ and H₂O; incomplete combustion yields CO and/or C (soot). The general equations for alkanes: CₙH₂ₙ₊₂ + (1.5n+0.5)O₂ → nCO₂ + (n+1)H₂O. In IB, you should be able to balance combustion equations and discuss environmental implications such as carbon monoxide toxicity and the enhanced greenhouse effect.
烷烃和醇是常见的燃料。在过量氧气中完全燃烧生成 CO₂ 和 H₂O；不完全燃烧产生 CO 和/或 C（炭黑）。烷烃的燃烧通式：CₙH₂ₙ₊₂ + (1.5n+0.5)O₂ → nCO₂ + (n+1)H₂O。在 IB 中，学生应能配平燃烧方程式并讨论环境影响，如一氧化碳的毒性和增强的温室效应。
11. Benzene and Resonance Stability (HL) | 苯与共振稳定性 (HL)
Benzene, C₆H₆, is an aromatic hydrocarbon with a ring of six carbon atoms and delocalised π electrons. The Kekulé structure with alternating single and double bonds does not reflect reality; all C–C bonds are identical with a bond order of 1.5. Evidence includes equal bond lengths and the lack of addition reactions typical of alkenes – benzene prefers electrophilic substitution to preserve aromatic stability. The delocalisation energy (resonance energy) makes benzene more stable than the hypothetical cyclohexatriene.
苯（C₆H₆）是一种芳香烃，具有六元碳环和离域 π 电子。凯库勒提出的单双键交替结构并不能反映真实情况；所有的 C–C 键均等，键级为 1.5。证据包括键长相等以及苯不发生类似烯烃的加成反应——苯更倾向于亲电取代以保持芳香稳定性。离域能（共振能）使苯比假想的环己三烯更加稳定。
12. Infrared Spectroscopy: Reading Molecular Fingerprints (HL & SL Option) | 红外光谱：解读分子指纹 (HL 与 SL 选修)
Infrared (IR) spectroscopy identifies functional groups by detecting bond vibrations. Major absorptions to remember: O–H (alcohols, broad ~3200–3600 cm⁻¹), C=O (~1700 cm⁻¹), C–H (~2900 cm⁻¹), and C–O (~1000–1300 cm⁻¹). The fingerprint region (<1500 cm⁻¹) is unique to each molecule. In data analysis questions, IB expects you to match absorption peaks to the corresponding bonds and deduce the likely functional groups present.
红外 (IR) 光谱通过检测化学键的振动来识别官能团。需记住的主要吸收峰：O–H（醇，宽峰约 3200–3600 cm⁻¹）、C=O（约 1700 cm⁻¹）、C–H（约 2900 cm⁻¹）和 C–O（约 1000–1300 cm⁻¹）。指纹区（<1500 cm⁻¹）对每种分子都是唯一的。在数据分析题中，IB 期待你将吸收峰与相应化学键匹配，并推断出可能存在的官能团。
Broad O–H at 3300 cm⁻¹ → alcohol or carboxylic acid; sharp C=O at 1720 cm⁻¹ → carbonyl compound.
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