📚 IB Chemistry: Functional Groups and Classification of Organic Compounds | IB化学：官能团与化合物分类
Organic chemistry is the study of carbon-based compounds, and the concept of functional groups is the key that unlocks the entire subject. In IB Chemistry, students must be able to recognise, name, and predict the properties of compounds based on the functional groups they contain. This article will provide a structured summary of the main functional groups found in the IB syllabus, how they determine compound classification, and how to apply this knowledge to exam questions.
有机化学是对碳基化合物的研究，而官能团这一概念正是理解整个学科的关键。在IB化学课程中，学生必须能够识别、命名，并根据化合物所含的官能团来预测其性质。本文将系统地总结IB考纲中的主要官能团、它们如何决定化合物的分类，以及如何将这些知识应用到考试问题中。
1. What Are Functional Groups? | 什么是官能团？
A functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. For example, the hydroxyl group (-OH) gives alcohols their ability to form hydrogen bonds and to undergo oxidation or esterification.
官能团是分子内一组特定的原子，它决定了该分子特有的化学反应。例如，羟基（-OH）使醇类具有形成氢键的能力，并能发生氧化反应或酯化反应。
The presence of a functional group also allows chemists to classify a compound into a particular family or homologous series. All members of a homologous series share the same functional group and general formula, but differ by a repeating -CH₂- unit.
官能团的存在也使化学家能够将化合物归入特定的家族或同系列。同一同系列的所有成员共享相同的官能团和通式，但相差一个重复的-CH₂-单元。
In IB Chemistry, you are expected to know the structures, names, and key reactions of alkanes, alkenes, alkynes, arenes, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines, and amides.
在IB化学中，你需要掌握烷烃、烯烃、炔烃、芳香烃、醇类、醚类、醛类、酮类、羧酸、酯类、胺类和酰胺的结构、命名及主要反应。
2. The Core Functional Groups in IB Chemistry | IB化学中的核心官能团
The table below summarises the main functional groups, their general structures, and representative examples. You should be able to quickly identify each group from a displayed or condensed molecular formula.
下表总结了主要官能团、其一般结构以及代表性实例。你应该能够从展开式或缩写的分子式中快速识别出每个官能团。
| Functional Group 官能团 | Structure (R = alkyl) 结构（R = 烷基） | Example 实例 |
|---|---|---|
| Alkane 烷烃 | C-C single bond (R-H) C-C单键 |
Ethane C₂H₆ 乙烷 |
| Alkene 烯烃 | C=C double bond C=C双键 |
Ethene C₂H₄ 乙烯 |
| Alkyne 炔烃 | C≡C triple bond C≡C三键 |
Ethyne C₂H₂ 乙炔 |
| Haloalkane 卤代烷烃 | R-X (X = F, Cl, Br, I) 卤素原子取代 |
Chloroethane CH₃CH₂Cl 氯乙烷 |
| Alcohol 醇 | R-OH (hydroxyl) 羟基 |
Ethanol C₂H₅OH 乙醇 |
| Ether 醚 | R-O-R’ (alkoxy) 烷氧基 |
Methoxyethane CH₃OCH₂CH₃ 甲乙醚 |
| Aldehyde 醛 | R-CHO (carbonyl + H) 醛基 |
Ethanal CH₃CHO 乙醛 |
| Ketone 酮 | R-CO-R’ (carbonyl + 2 C) 酮基 |
Propanone CH₃COCH₃ 丙酮 |
| Carboxylic acid 羧酸 | R-COOH 羧基 |
Ethanoic acid CH₃COOH 乙酸 |
| Ester 酯 | R-COO-R’ 酯基 |
Ethyl ethanoate CH₃COOCH₂CH₃ 乙酸乙酯 |
| Amine 胺 | R-NH₂ (primary) 氨基 |
Ethylamine CH₃CH₂NH₂ 乙胺 |
| Amide 酰胺 | R-CONH₂ 酰胺基 |
Ethanamide CH₃CONH₂ 乙酰胺 |
3. Homologous Series and General Formulas | 同系列与通式
A homologous series is a family of compounds with the same functional group and the same general formula. For example, all alkanes have the general formula CₙH₂ₙ₊₂, where n is the number of carbon atoms.
同系列是一组具有相同官能团和相同通式的化合物。例如，所有烷烃的通式都是CₙH₂ₙ₊₂，其中n是碳原子数。
You must be able to write and interpret these formulas:
你必须能够书写并理解以下这些通式：
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Alkanes: CₙH₂ₙ₊₂
烷烃：CₙH₂ₙ₊₂
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Alkenes (one double bond): CₙH₂ₙ
烯烃（含一个双键）：CₙH₂ₙ
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Alcohols (monohydric): CₙH₂ₙ₊₂O
醇（一元醇）：CₙH₂ₙ₊₂O
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Aldehydes and ketones (saturated): CₙH₂ₙO
饱和醛和酮：CₙH₂ₙO
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Carboxylic acids (monoacidic): CₙH₂ₙO₂
一元羧酸：CₙH₂ₙO₂
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Primary amines: CₙH₂ₙ₊₃N
伯胺：CₙH₂ₙ₊₃N
The general formula is a powerful tool: it allows you to determine the molecular formula for any homologue if you know the number of carbons, and to classify an unknown organic compound from its molecular formula.
通式是一个强大的工具：只要知道碳原子数目，你就能确定任意同系物的分子式；同时还可以根据分子式对未知有机化合物进行分类。
4. Naming Compounds: Prefixes and Suffixes | 命名规则：前缀与后缀
In IUPAC nomenclature, the suffix of a compound name indicates the highest-priority functional group present. The priority order (high to low) in IB is: carboxylic acid > ester > amide > aldehyde > ketone > alcohol > amine > ether > haloalkane > alkene > alkyne.
在国际纯粹与应用化学联合会（IUPAC）命名法中，化合物名称的后缀表示其优先级最高的官能团。IB中从高到低的优先级顺序为：羧酸 > 酯 > 酰胺 > 醛 > 酮 > 醇 > 胺 > 醚 > 卤代烃 > 烯烃 > 炔烃。
Here are the key naming patterns:
以下是关键的命名模式：
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Alkanes: suffix -ane (e.g., butane)
烷烃：后缀-ane（如丁烷 butane）
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Alkenes: suffix -ene with a locant (e.g., but-2-ene)
烯烃：后缀-ene并标明位置（如丁-2-烯 but-2-ene）
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Alcohols: suffix -ol (e.g., propan-2-ol)
醇：后缀-ol（如丙-2-醇 propan-2-ol）
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Aldehydes: suffix -al (e.g., pentanal)
醛：后缀-al（如戊醛 pentanal）
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Ketones: suffix -one with a locant (e.g., pentan-2-one)
酮：后缀-one并标明位置（如戊-2-酮 pentan-2-one）
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Carboxylic acids: suffix -oic acid (e.g., propanoic acid)
羧酸：后缀-oic acid（如丙酸 propanoic acid）
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Esters: alkyl (from alcohol) + oate (from acid), e.g., methyl propanoate
酯：烷基（来自醇）+ 醇改成的oate（来自酸），如丙酸甲酯 methyl propanoate
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Haloalkanes: prefix fluoro-, chloro-, bromo-, iodo- (e.g., 2-chlorobutane)
卤代烃：前缀fluoro-（氟）、chloro-（氯）、bromo-（溴）、iodo-（碘），如2-氯丁烷 2-chlorobutane
Always select the longest carbon chain that includes the principal functional group, and number the chain so that the functional group gets the lowest possible locant.
始终选择包含主要官能团的最长碳链作为主链，并给主链编号，使官能团获得尽可能小的位次数字。
5. Aliphatic vs Aromatic Compounds | 脂肪族与芳香族化合物
Organic compounds can be broadly divided into aliphatic and aromatic classes. Aliphatic compounds have open-chain or cyclic structures with no conjugated ring system; examples include alkanes, alkenes, alcohols, and carboxylic acids.
有机化合物大致可分为脂肪族和芳香族两类。脂肪族化合物具有开链或环状结构，没有共轭环系；例如烷烃、烯烃、醇和羧酸。
Aromatic compounds contain a benzene ring or a similar conjugated planar ring with delocalised π electrons. Benzene itself is a six-membered ring with the formula C₆H₆. The delocalisation makes the ring unusually stable, so aromatic compounds tend to undergo substitution reactions rather than addition.
芳香族化合物含有苯环或类似的具有离域π电子的共轭平面环。苯本身是六元环，分子式为C₆H₆。离域作用使该环异常稳定，因此芳香族化合物倾向于发生取代反应而不是加成反应。
Common aromatic compounds in IB include benzene, methylbenzene (toluene), and phenol (C₆H₅OH). Note that phenol is named as a separate class because the -OH group is attached directly to the ring; it behaves differently from a typical aliphatic alcohol.
IB中常见的芳香族化合物包括苯、甲苯（甲基苯）和苯酚（C₆H₅OH）。注意，苯酚被单独归类，因为-OH直接连在苯环上；其行为与典型的脂肪族醇不同。
For example, benzene undergoes electrophilic substitution (e.g., nitration) but not the addition reactions typical of alkenes.
例如，苯发生亲电取代反应（如硝化反应），而不会发生烯烃典型的加成反应。
6. Functional Group Interconversions | 官能团之间的相互转化
Understanding how functional groups can be converted into each other is central to organic synthesis. The following reactions are frequently tested in IB Chemistry Paper 2.
理解官能团之间如何相互转化是有机合成的核心。以下反应在IB化学Paper 2中经常考到。
First, oxidation of alcohols:
第一，醇的氧化反应：
RCH₂OH + [O] → RCHO + H₂O (primary alcohol → aldehyde)
RCH₂OH + 2[O] → RCOOH + H₂O (primary alcohol → carboxylic acid)
R₂CHOH + [O] → R₂C=O + H₂O (secondary alcohol → ketone)
Second, alkene hydration:
第二，烯烃的水合反应：
C₂H₄ + H₂O ⇌ C₂H₅OH (acid catalyst, steam)
Third, esterification:
第三，酯化反应：
RCOOH + R’OH ⇌ RCOOR’ + H₂O (conc. H₂SO₄, heat)
Fourth, nucleophilic substitution of haloalkanes:
第四，卤代烃的亲核取代反应：
RBr + NaOH → ROH + NaBr (aqueous, heat)
You should also know that aldehydes can be oxidised to carboxylic acids under reflux, whereas ketones do not undergo oxidation under these conditions.
你还应该知道，醛在回流条件下可以被氧化为羧酸，而酮在这种条件下不会被氧化。
7. Physical Properties and Functional Groups | 物理性质与官能团
Functional groups determine not only chemical reactivity but also physical properties such as boiling point, solubility, and polarity.
官能团不仅决定化学反应性，还决定物理性质，如沸点、溶解度和极性。
Alcohols and carboxylic acids form intermolecular hydrogen bonds, so they have significantly higher boiling points than alkanes or haloalkanes of similar molar mass.
醇和羧酸能形成分子间氢键，因此其沸点明显高于摩尔质量相近的烷烃或卤代烃。
Soluble organic compounds in water are typically those that can hydrogen bond with water: short-chain alcohols, aldehydes, ketones, carboxylic acids, and amines. As the hydrocarbon chain lengthens, solubility in water decreases because the non-polar tail dominates.
能溶于水的有机化合物通常是那些能和水形成氢键的：短链醇、醛、酮、羧酸和胺。随着烃链增长，溶解度在水中会下降，因为非极性的碳链逐渐占主导。
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Strongest intermolecular forces: carboxylic acids (H-bond + dimer formation), alcohols/amines (H-bond), aldehydes/ketones (dipole-dipole), alkanes/alkenes (van der Waals).
最强分子间作用力排序：羧酸（氢键+二聚体）、醇/胺（氢键）、醛/酮（偶极-偶极）、烷烃/烯烃（范德华力）。
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Small alcohols (e.g., ethanol) and small acids (e.g., ethanoic acid) are fully miscible with water.
小分子醇（如乙醇）和小分子酸（如乙酸）可与水完全混溶。
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Ethers are less polar than alcohols and tend to have lower boiling points, despite having the same molecular formula as an isomeric alcohol.
醚的极性低于醇，尽管与同分异构的醇具有相同分子式，其沸点往往更低。
8. Spectroscopic Identification of Functional Groups | 官能团的波谱鉴定
IB Chemistry includes the use of infrared (IR) spectroscopy and mass spectrometry to identify functional groups.
IB化学包括使用红外光谱和质谱来鉴定官能团。
In IR spectroscopy, different functional groups absorb infrared radiation at characteristic wavenumbers. The following absorption ranges are common in IB questions:
在红外光谱中，不同的官能团在特征波数处吸收红外辐射。以下是IB题目中常见的吸收范围：
| Functional Group 官能团 | IR Wavenumber (cm⁻¹) 波数 |
|---|---|
| O-H (alcohol) 羟基（醇） | 3200–3600 (broad) |
| N-H (amine) 氨基 | 3300–3500 (medium) |
| C=O (aldehyde/ketone/carboxylic acid) 羰基 | 1630–1750 (strong) |
| C-O (alcohol/ester) 碳氧单键 | 1000–1300 |
| C=C (alkene) 碳碳双键 | 1620–1680 (variable) |
Mass spectrometry can complement IR: the molecular ion peak gives the relative molecular mass, and fragment peaks can suggest the presence of certain groups. For example, a loss of 17 (OH) from a molecular ion suggests an alcohol; a loss of 29 (CHO or C₂H₅) may indicate an aldehyde or an ethyl group.
质谱可以补充红外信息：分子离子峰给出相对分子质量，碎片峰则可提示某些基团的存在。例如，分子离子失去17（OH）表明可能有醇；失去29（CHO或C₂H₅）则可能指示醛或乙基。
9. Common Mistakes and Exam Pitfalls | 常见错误与考试陷阱
Students often lose marks in IB exams due to a few recurring misconceptions. Being aware of these will help you avoid them.
学生在IB考试中常因几个反复出现的误解而失分。了解这些可以帮助你避免错误。
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Confusing aldehydes and ketones: Aldehydes have a terminal carbonyl carbon bonded to at least one H atom, so they are easily oxidised. Ketones have the carbonyl carbon bonded to two carbon groups and are not easily oxidised.
混淆醛与酮：醛的羰基碳在链端，且至少连有一个氢原子，因此容易被氧化。酮的羰基碳连接两个碳原子，不易被氧化。
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Mixing up carboxylic acids and esters: Carboxylic acids contain an -OH group attached to the carbonyl carbon (COOH); esters contain an -OR group (COOR). In naming, the acid suffix is ‘-oic acid’ while the ester suffix is ‘-oate’.
区分羧酸和酯：羧酸含有连在羰基碳上的-OH（即COOH）；酯含有-OR基团（即COOR）。命名时，酸的后缀是’-oic acid’，而酯的后缀是’-oate’。
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Wrong priority in nomenclature: For a compound containing both an -OH and a C=O, such as a hydroxyketone, the ketone suffix (-one) takes priority over the alcohol suffix (-ol). The -OH is then named as a prefix ‘hydroxy-‘.
命名中优先级顺序错误：对于同时含有-OH和C=O的化合物（如羟基酮），酮的后缀（-one）优先于醇的后缀（-ol），此时-OH作为前缀’hydroxy-‘命名。
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Assuming all -OH compounds are alcohols: Phenol (C₆H
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