📚 IGCSE OCR Chemistry: Alcohols Masterclass | IGCSE OCR 化学：醇 考点精讲
Alcohols are a fascinating and important class of organic compounds, containing the hydroxyl functional group. For your OCR IGCSE Chemistry exam, understanding their structure, naming, properties, and reactions is essential. This guide covers all you need to know about alcohols, from methanol to butanol, their manufacture, and chemical behaviour.
醇是一类迷人且重要的有机化合物，都含有羟基官能团。在 OCR IGCSE 化学考试中，理解它们的结构、命名、性质及反应至关重要。本指南涵盖从甲醇到丁醇、醇的制备及其化学行为，助你掌握全部考点。
1. What Are Alcohols? Functional Group & Homologous Series | 什么是醇？官能团与同系物
Alcohols are organic compounds characterised by the presence of one or more hydroxyl (–OH) functional groups attached to a carbon chain. In IGCSE, we focus on the homologous series of alkanols with the general formula CₙH₂ₙ₊₁OH (or CₙH₂ₙ₊₂O). The hydroxyl group is what defines the chemistry of alcohols. The first four members are methanol (CH₃OH), ethanol (C₂H₅OH), propanol (C₃H₇OH) and butanol (C₄H₉OH). They form a homologous series, meaning they have the same functional group, a general formula, and a gradation in physical properties.
醇是含有连接在碳链上的一个或多个羟基(–OH)官能团的有机化合物。在IGCSE阶段，我们重点学习烷醇同系物，通式为CₙH₂ₙ₊₁OH（或CₙH₂ₙ₊₂O）。羟基决定了醇的化学性质。前四个成员是甲醇(CH₃OH)、乙醇(C₂H₅OH)、丙醇(C₃H₇OH)和丁醇(C₄H₉OH)。它们形成同系物，意味着它们具有相同的官能团、通式以及物理性质的渐变。
2. Naming Alcohols (IUPAC) | 醇的命名
The IUPAC name of an alcohol is derived by replacing the final -e of the parent alkane with -ol, and using a number to indicate the position of the hydroxyl group if necessary. For example: Methane → Methanol (no number needed). Ethane → Ethanol. Propane: if hydroxyl on carbon-1, propan-1-ol; if on carbon-2, propan-2-ol. Similarly for butanol: butan-1-ol, butan-2-ol, etc. The hydroxyl group takes priority in numbering.
醇的IUPAC命名是将母体烷烃名称末尾的“烷”改为“醇”，如果需要，用数字标明羟基的位置。例如：甲烷→甲醇；乙烷→乙醇；丙烷：若羟基在1号碳上，则为丙-1-醇，若在2号碳上则为丙-2-醇。丁醇类似：丁-1-醇，丁-2-醇等。编号时羟基优先级最高。
3. Structural Formulas & Isomerism | 结构式与同分异构现象
Each alcohol can be represented by its molecular formula, full structural formula (showing all bonds), or displayed formula. Isomerism occurs from propanol onwards. Propanol has two isomers: propan-1-ol and propan-2-ol. Butanol has four structural isomers: butan-1-ol, butan-2-ol, 2-methylpropan-1-ol, and 2-methylpropan-2-ol. Recognising isomers is important for naming and reactions.
每种醇都可以用分子式、完整的结构式或显示式表示。从丙醇开始出现同分异构现象。丙醇有两种异构体：丙-1-醇和丙-2-醇。丁醇有四种结构异构体：丁-1-醇、丁-2-醇、2-甲基丙-1-醇和2-甲基丙-2-醇。识别异构体对命名和反应很重要。
4. Physical Properties of Alcohols | 醇的物理性质
Alcohol molecules can form hydrogen bonds with each other because the –OH group is polar. This gives them higher boiling points than alkanes of similar molecular size.
由于–OH基团具有极性，醇分子之间可以形成氢键。这使得它们的沸点比分子大小相近的烷烃高。
As the carbon chain length increases, the hydrophobic hydrocarbon part grows, reducing water solubility. Methanol, ethanol and propanol are completely miscible with water, while butanol is only sparingly soluble.
随着碳链增长，疏水性的烃基部分增大，水溶性降低。甲醇、乙醇和丙醇与水完全混溶，而丁醇仅微溶。
Volatility decreases with increasing molecular size: methanol and ethanol are quite volatile liquids at room temperature. Most lower alcohols have a characteristic smell.
挥发性随分子量增大而降低：甲醇和乙醇在室温下是较易挥发的液体。低级醇通常具有特殊气味。
5. Manufacture of Ethanol: Fermentation | 乙醇的制造：发酵法
Fermentation produces ethanol from sugar (glucose) using yeast. The conditions required are a temperature of 30–40 °C and an anaerobic (absence of oxygen) environment. Yeast supplies enzymes that convert glucose into ethanol and carbon dioxide.
发酵法利用酵母将糖(葡萄糖)转化为乙醇。条件：温度30–40 ℃，厌氧(无氧)环境。酵母提供酶，将葡萄糖转化为乙醇和二氧化碳。
C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂
This is a batch process, producing a dilute aqueous solution of ethanol (around 10–15%), which can be concentrated by fractional distillation. The raw material is renewable (sugar cane, maize, etc.), but the process is relatively slow.
这是一个分批过程，得到约10–15%的稀乙醇溶液，可通过分馏浓缩。原料可再生（甘蔗、玉米等），但过程较慢。
6. Manufacture of Ethanol: Hydration of Ethene | 乙醇的制造：乙烯水合法
Ethene (C₂H₄) reacts with steam (H₂O) in the presence of a phosphoric acid (H₃PO₄) catalyst at high temperature (around 300 °C) and high pressure (60–70 atm) to produce ethanol directly.
乙烯(C₂H₄)与水蒸气(H₂O)在磷酸(H₃PO₄)催化剂作用下，于高温(约300 ℃)和高压(60–70 atm)下直接合成乙醇。
C₂H₄ + H₂O ⇌ C₂H₅OH
This is a continuous process, producing pure ethanol in high yield. The ethene is obtained from crude oil (a non‑renewable resource) via cracking.
这是一个连续过程，可高产率地得到纯乙醇。乙烯来自石油(不可再生资源)通过裂解获得。
7. Comparing Fermentation & Hydration | 发酵法与水合法对比
The two industrial methods for making ethanol have distinct advantages and disadvantages. The table below summarises the key differences.
这两种工业制造乙醇的方法各有利弊。下表总结了关键差异。
| Feature | Fermentation | Hydration of Ethene |
|---|---|---|
| Raw materials | Sugar/starch (renewable) | Ethene from crude oil (non-renewable) |
| Type of process | Batch | Continuous |
| Temperature & pressure | 30–40 °
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