📚 Alcohols: IB & Edexcel Chemistry Revision Notes | IB Edexcel 化学：醇 考点精讲
Alcohols are an essential functional group in organic chemistry, featuring the hydroxyl (–OH) group attached to a saturated carbon atom. For both IB and Edexcel A-Level Chemistry, you need to master their structure, classification, physical properties, preparation, and a wide range of reactions including oxidation, elimination, and esterification. This revision guide systematically covers all key assessment points with bilingual explanations, helping you build a solid understanding for exams.
醇是有机化学中一类重要的官能团化合物，其特征是羟基（–OH）连接在饱和碳原子上。无论是 IB 还是 Edexcel A-Level 化学，你都需要掌握醇的结构、分类、物理性质、制备方法以及氧化、消去、酯化等一系列反应。这份考点精讲以中英双语系统梳理所有重点，助你扎实备考。
1. Structure and Functional Group | 结构与官能团
Alcohols contain the hydroxyl functional group, –OH, bonded to an sp³ hybridised carbon atom. The oxygen atom has two lone pairs of electrons, giving the molecule a bent geometry around the oxygen (approximately 104.5° bond angle in water and similar in alcohols). The polar C–O and O–H bonds are responsible for the characteristic physical and chemical properties of alcohols.
醇含有羟基官能团 –OH，连接在 sp³ 杂化的碳原子上。氧原子有两对孤对电子，使其周围的几何形状呈弯曲型（水中的键角约为 104.5°，醇中类似）。极性的 C–O 键和 O–H 键是醇类物理和化学性质的基础。
2. Classification of Alcohols | 醇的分类
Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) based on the number of carbon atoms directly attached to the carbon bearing the –OH group. A primary alcohol has the –OH on a carbon bonded to only one other carbon (e.g., ethanol, CH₃CH₂OH). A secondary alcohol has the –OH on a carbon bonded to two other carbons (e.g., propan-2-ol, CH₃CHOHCH₃). A tertiary alcohol has the –OH on a carbon bonded to three other carbons (e.g., 2-methylpropan-2-ol, (CH₃)₃COH).
根据连接羟基的碳原子上所连碳原子数，醇可分为伯醇（1°）、仲醇（2°）和叔醇（3°）。伯醇的 –OH 所在碳只与一个其他碳相连（如乙醇 CH₃CH₂OH）。仲醇的 –OH 所在碳与两个其他碳相连（如丙-2-醇 CH₃CHOHCH₃）。叔醇的 –OH 所在碳与三个其他碳相连（如 2-甲基丙-2-醇 (CH₃)₃COH）。
3. Nomenclature of Alcohols | 醇的命名
In IUPAC nomenclature, alcohols are named by replacing the final '-e' of the parent alkane with '-ol'. The chain is numbered to give the hydroxyl group the lowest possible locant. For example, CH₃CH₂CH₂OH is propan-1-ol. When higher priority groups are present, the –OH is named as a 'hydroxy' substituent. Common names are still used for simple alcohols, like methyl alcohol for methanol.
在 IUPAC 命名法中，醇是由母体烷烃去掉词尾的 '-e' 加上 '-ol' 来命名的。主链编号应使羟基的位置编号尽可能小。例如 CH₃CH₂CH₂OH 为丙-1-醇。当分子中存在更优先的官能团时，羟基作为“羟基”取代基命名。简单醇仍常用俗名，如甲醇称为 methyl alcohol。
4. Physical Properties | 物理性质
Alcohols have relatively high boiling points compared to alkanes of similar molar mass due to intermolecular hydrogen bonding between –OH groups. Solubility in water decreases as the length of the non-polar hydrocarbon chain increases. Methanol, ethanol, and propanol are miscible with water in all proportions, whereas longer-chain alcohols are only slightly soluble. The hydrogen bonding also makes alcohols good solvents for polar substances.
与相似摩尔质量的烷烃相比，醇的沸点较高，这是因为醇分子间可形成氢键。在水中的溶解度随非极性碳链增长而降低。甲醇、乙醇和丙醇与水可以任意比例混溶，而长链醇仅微溶于水。氢键也使醇成为极性物质的良好溶剂。
5. Preparation of Alcohols | 醇的制备
laboratory and industrial methods for preparing alcohols include: (a) Hydration of alkenes – ₃PO₄) at high temperature and pressure, e.g., ethene → ethanol. (b) Fermentation of sugars – es convert glucose into ethanol and carbon dioxide under anaerobic conditions at around 30–40 °C. (c) Reduction of carbonyl compounds – alcohols using reducing agents such as NaBH₄ or LiAlH₄. (d) Hydrolysis of halogenoalkanes – reflux with aqueous NaOH or KOH.
醇的主要实验室与工业制备方法包括：(a) 烯烃水合法——在磷酸等酸性催化剂、高温高压下，烯烃与水蒸气加成，如乙烯制乙醇。(b) 糖类发酵法——在 30–40 °C 厌氧条件下，酵母酶将葡萄糖转化为乙醇和二氧化碳。(c) 羰基化合物还原——用 NaBH₄ 或 LiAlH₄ 等还原剂将醛还原为伯醇，将酮还原为仲醇。(d) 卤代烷水解——与 NaOH 或 KOH 水溶液回流。
6. Combustion of Alcohols | 醇的燃烧
l: C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O. The enthalpy of combustion increases with the number of carbon atoms in the alcohol chain. Sooty flames may appear with longer-chain alcohols due to incomplete combustion.
醇在过量氧气中燃烧生成二氧化碳和水，并释放大量能量，因此可用作燃料。以乙醇为例：C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O。燃烧焓随醇的碳链增长而增加。长链醇可能因不完全燃烧而产生带烟灰的火焰。
7. Oxidation of Alcohols | 醇的氧化反应
Oxidation is one of the most important and commonly examined reactions of alcohols. Primary alcohols are oxidised first to aldehydes, and upon further oxidation to carboxylic acids. Secondary alcohols are oxidised to ketones. Tertiary alcohols resist oxidation under normal conditions because there is no hydrogen atom on the carbon bearing the –OH. The typical oxidising agent is acidified potassium dichromate(VI), K₂Cr₂O₇/H⁺, which changes colour from orange to green as Cr(VI) is reduced to Cr(III). To isolate the aldehyde from a primary alcohol, distillation is used to remove it from the reaction mixture before further oxidation occurs; for full oxidation to the carboxylic acid, heating under reflux is employed.
氧化是醇最重要、最常考的反应之一。伯醇先被氧化为醛，进一步氧化生成羧酸。仲醇被氧化为酮。叔醇在通常条件下不易被氧化，因为连接 –OH 的碳原子上没有氢。常用氧化剂为酸化重铬酸钾 K₂Cr₂O₇/H⁺，反应中橙色变为绿色（Cr(VI) 被还原为 Cr(III)）。要从伯醇制备醛，需采用蒸馏，及时将醛从反应体系中分离以防止进一步氧化；若要彻底氧化为羧酸，则需加热回流。
8. Dehydration (Elimination) of Alcohols | 醇的消去（脱水）反应
Alcohols undergo dehydration to form alkenes when heated with a concentrated acid catalyst such as concentrated H₂SO₄ or H₃PO₄, or by passing vapour over hot aluminium oxide (Al₂O₃) at about 350 °C. This is an elimination reaction (loss of a water molecule). For unsymmetrical alcohols, more than one alkene product is possible, and Zaitsev's rule predicts the more substituted alkene as the major product. For example, butan-2-ol yields mainly but-2-ene rather than but-1-ene.
醇在浓硫酸或浓磷酸等强酸催化下加热，或通过蒸气通过约 350 °C 的热氧化铝（Al₂O₃），可发生脱水反应生成烯烃。这是一个消去反应（失去一分子水）。对于不对称的醇，可能生成多种烯烃产物，根据扎伊采夫规则，取代更多的烯烃为主要产物。例如丁-2-醇主要生成丁-2-烯而非丁-1-烯。
9. Esterification | 酯化反应
Alcohols react with carboxylic acids in the presence of a strong acid catalyst (commonly concentrated H₂SO₄) to form esters and water. This is a condensation reaction and is reversible. Esters have characteristic sweet, fruity smells and are used as flavourings and solvents. The reaction is typically carried out by heating under reflux. For example, ethanol and ethanoic acid produce ethyl ethanoate: CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O.
醇与羧酸在强酸催化（通常是浓硫酸）下反应生成酯和水，属于缩合反应且可逆。酯具有特征性的果香味，用作香料和溶剂。该反应通常加热回流进行。例如乙醇和乙酸反应生成乙酸乙酯：CH₃COOH + C₂H₅OH ⇌ CH₃COOC₂H₅ + H₂O。
10. Reaction with Sodium and Halogenating Agents | 与钠及卤化试剂的反应
s: 2C₂H₅OH + 2Na → 2C₂H₅O⁻Na⁺ + H₂. Alcohols also react with phosphorus halides (PCl₅, PBr₃, or P/I₂) to replace the – est (ZnCl₂/HCl) can distinguish between primary, secondary, and tertiary alcohols based on the rate of cloudiness formation due to the immiscible alkyl chloride produced.
醇与活泼金属如钠反应生成醇盐和氢气，类似于水与钠的反应但较缓和：2C₂H₅OH + 2Na → 2C₂H₅O⁻Na⁺ + H₂。醇还能与卤化磷（PCl₅、PBr₃ 或 P/I₂）反应，将 –OH 取代为卤原子，生成卤代烷。例如室温下与 PCl₅ 反应：C₂H₅OH + PCl₅ → C₂H₅Cl + POCl₃ + HCl。卢卡斯试剂（ZnCl₂/浓盐酸）可通过观察不溶于水的氯代烷出现浑浊的速率，来区分伯、仲、叔醇。
11. Tests for Alcohols and Summary of Oxidation Trends | 醇的检验与氧化规律总结
The two most common tests for alcohols are: (i) Acidified potassium dichromate(VI) – warm with the alcohol; primary and secondary alcohols give a colour change from orange to green, while tertiary alcohols show no reaction. (ii) Lucas test – tertiary alcohols produce immediate cloudiness, secondary alcohols within about 5 minutes upon warming, and primary alcohols show no reaction at room temperature. The reactivity towards oxidation and substitution is closely linked to the alcohol classification, which is a key exam focus.
醇的两种最常见检验方法是：(i) 酸化重铬酸钾(VI)——与醇共热，伯醇和仲醇能使溶液由橙色变为绿色，叔醇无反应。(ii) 卢卡斯试验——叔醇立即出现浑浊，仲醇温热后约 5 分钟变浑浊，伯醇室温下无反应。氧化和取代反应的活性与醇的分类密切相关，这是考试的重点考查方向。
12. Summary Reaction Table | 反应汇总表
| Reaction / 反应 | Reagents & Conditions / 试剂与条件 | Product / 产物 | Notes / 备注 |
|---|---|---|---|
| Combustion / 燃烧 | Excess O₂, ignite / 过量氧气，点燃 | CO₂ + H₂O | Exothermic; used as fuel / 放热，用作燃料 |
| Oxidation: 1° alcohol / 伯醇氧化 | K₂Cr₂O₇/H⁺, distil (for aldehyde) or reflux (for acid) / 酸化重铬酸钾，蒸馏得醛，回流得酸 | Aldehyde → Carboxylic acid / 醛 → 羧酸 | Orange → green colour change / 橙色变绿色 |
| Oxidation: 2° alcohol / 仲醇氧化 | K₂Cr₂O₇/H⁺, reflux / 酸化重铬酸钾，回流 | Ketone / 酮 | No further oxidation / 不再进一步氧化 |
| Dehydration / 脱水 | Conc. H₂SO₄ or Al₂O₃, heat / 浓硫酸或氧化铝，加热 | Alkene(s) / 烯烃 | Elimination; Zaitsev rule / 消去反应，扎伊采夫规则 |
| Esterification / 酯化 | Carboxylic acid + conc. H₂SO₄, reflux / 羧酸+浓硫酸，回流 | Ester + water / 酯 + 水 | Reversible; sweet odour / 可逆，有果香味 |
| Reaction with Na / 与钠反应 | Na metal, room temp. / 金属钠，室温 | Alkoxide + H₂ / 醇盐 + 氢气 | Bubbles of gas / 有气泡产生 |
| Halogenation / 卤化 | PCl₅, or PBr₃, or P/I₂ / 五氯化磷等 | Halogenoalkane / 卤代烷 | Substitution; used in Lucas test / 取代反应，卢卡斯试验中用 |
Published by TutorHao | Chemistry Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图