📚 Alcohols, Esters and Carboxylic Acids | 醇、酯和羧酸
Alcohols, carboxylic acids and esters are three closely related families of oxygen-containing organic compounds. Their chemistry is interwoven through reactions such as oxidation, esterification and hydrolysis, making them a cornerstone of A-Level organic chemistry. Understanding their structures, properties and transformations provides a foundation for exploring biochemistry, industrial processes and synthetic pathways.
醇、羧酸和酯是三种密切相关的含氧有机化合物家族。它们的化学通过氧化、酯化和水解等反应相互联系，成为A-Level有机化学的基石。理解它们的结构、性质与转化关系，为探索生物化学、工业过程和合成路线奠定了基础。
1. Introducing the Functional Groups | 官能团概览
Alcohols contain the hydroxyl group —OH bonded to a saturated carbon atom. The general formula for saturated monohydric alcohols is CₙH₂ₙ₊₁OH.
醇含有与饱和碳原子相连的羟基 —OH。饱和一元醇的通式为 CₙH₂ₙ₊₁OH。
Carboxylic acids are characterised by the carboxyl group —COOH, which consists of a carbonyl (C=O) and a hydroxyl (— s CₙH₂ₙ₊₁COOH, although the simplest member, methanoic acid (HCOOH), lacks an alkyl chain.
羧酸的特征官能团是羧基 —COOH，它由同一碳原子上的羰基 (C=O) 和羟基 (—OH) 组成。其通式为 CₙH₂ₙ₊₁COOH，但最简单的甲酸 (HCOOH) 没有烷基链。
Esters are derived from the reaction of an alcohol and a carboxylic acid. They contain the ester linkage —COO—, where the carbonyl carbon is also attached to an —OR group. A typical ester has the formula RCOOR′.
酯来源于醇与羧酸的反应。它们含有酯键 —COO—，羰基碳同时连接 —OR 基团。典型酯的通式为 RCOOR′。
2. Naming and Classification of Alcohols, Carboxylic Acids and Esters | 醇、羧酸和酯的命名与分类
For alcohols, the IUPAC name replaces the -e of the parent alkane with -ol, and a number indicates the position of the —OH group. For instance, CH₃CH₂OH is ethanol and CH₃CH(OH)CH₃ is propan-2-ol.
醇的 IUPAC 命名是将母体烷烃的 -e 替换为 -ol，并用数字标明 —OH 的位置。例如 CH₃CH₂OH 为乙醇，CH₃CH(OH)CH₃ 为丙-2-醇。
Carboxylic acids are named by replacing the -e of the corresponding alkane with -oic acid. Thus, HCOOH is methanoic acid and CH₃CH₂COOH is propanoic acid. The carbon of the carboxyl group is always position 1.
羧酸是将相应烷烃的 -e 替换为 -oic acid 来命名。因此 HCOOH 为甲酸，CH₃CH₂COOH 为丙酸。羧基的碳原子总是位于 1 号位。
Esters are named as alkyl alkanoates. The alkyl portion comes from the alcohol and the alkanoate from the carboxylic acid. For example, CH₃COOCH₂CH₃ is ethyl ethanoate.
酯的命名采用“某醇基某酸酯”。烷基部分来自醇，酸根部分来自羧酸。例如 CH₃COOCH₂CH₃ 为乙酸乙酯。
Alcohols are classified as primary (1°), secondary (2°) or tertiary (3°) depending on the number of carbon atoms attached to the carbon bearing the —OH group. A primary alcohol has the —OH on a carbon attached to one other carbon, a secondary alcohol on a carbon attached to two, and a tertiary alcohol on a carbon attached to three.
醇根据连接 —OH 的碳原子上所连碳原子数分为伯醇 (1°)、仲醇 (2°) 和叔醇 (3°)。伯醇的 —OH 连在只与一个碳相连的碳上，仲醇连在与两个碳相连的碳上，叔醇则连在与三个碳相连的碳上。
3. Structure and Bonding in Alcohols | 醇的结构与成键
The oxygen atom in an alcohol is sp³ hybridised, giving a bent shape around the O atom with a C—O—H bond angle of approximately 104.5°, similar to water. The O—H bond is polar due to the electronegativity difference, making the hydrogen slightly positive.
醇中的氧原子为 sp³ 杂化，使得氧原子周围呈弯曲形状，C—O—H 键角约为 104.5°，与水分子类似。由于电负性差异，O—H 键具有极性，氢原子带有部分正电荷。
The C—O bond is also polar, and the lone pairs on oxygen play a crucial role in hydrogen bonding and nucleophilic reactions.
C—O 键也具有极性，氧上的孤对电子在氢键和亲核反应中起关键作用。
4. Physical Properties: Boiling Points and Solubility | 物理性质：沸点和溶解度
s. For example, ethanol (Mᵣ = 46) boils at 78 °C, whereas propane (Mᵣ = 44) boils at −42 °C.
醇的沸点明显高于分子量相近的烷烃，这是因为醇分子间能够形成氢键。例如，乙醇 (Mᵣ = 46) 沸点为 78 °C，而丙烷 (Mᵣ = 44) 沸点为 −42 °C。
Short-chain alcohols are miscible with water in all proportions because the hydroxyl group can form hydrogen bonds with water molecules. As the hydrocarbon chain lengthens, the hydrophobic nature of the alkyl group dominates, and solubility decreases.
短链醇可以和水以任意比例混溶，因为羟基能够与水分子形成氢键。随着烃链增长，烷基的疏水性增强，溶解度下降。
mers. Ethanoic acid (Mᵣ = 60) boils at 118 °C, while propan-1-ol (Mᵣ = 60) boils at 97 °C.
羧酸的沸点比同碳数的醇更高，因为它们形成牢固的氢键二聚体。乙酸 (Mᵣ = 60) 沸点为 118 °C，而丙-1-醇 (Mᵣ = 60) 沸点为 97 °C。
Esters, lacking an — the corresponding alcohols and carboxylic acids. Ethyl ethanoate (Mᵣ = 88) boils at 77 °C.
酯没有 —OH 基团，自身不能形成强氢键，其沸点低于相应的醇和羧酸。乙酸乙酯 (Mᵣ = 88) 沸点为 77 °C。
5. Preparation of Alcohols | 醇的制备
am in the presence of a phosphoric acid catalyst at about 300 °C and 60 atm: CH₂=CH₂ + H₂O ⇌ . This is a continuous process, but the conversion is limited by the equilibrium position.
工业制乙醇的一种方法是乙烯直接水化。乙烯与水蒸气在磷酸催化剂、约 300 °C 和 60 atm 下反应：CH₂=CH₂ + H₂O ⇌ CH₃CH₂OH。这是连续化过程，但受平衡限制转化率不高。
aerobically at about 35 °C and produces a dilute aqueous solution, which is then concentrated by fractional distillation.
葡萄糖在酵母作用下发酵产生乙醇和二氧化碳：C₆H₁₂O₆ → 2 CH₃CH₂OH + 2 CO₂。发酵在约 35 °C 的厌氧条件下进行，得到稀乙醇溶液，再通过分馏浓缩。
. This method works well for primary and secondary halogenoalkanes, though elimination may compete with secondary substrates.
醇也可在实验室通过卤代烷与热碱水溶液的水解制得，例如 CH₃CH₂Br + OH⁻ → CH₃CH₂OH + Br⁻。该方法对伯卤代烷和仲卤代烷有效，但仲卤代烷可能伴随消除反应。
ols using reducing agents such as NaBH₄ or LiAlH₄. For instance, CH₃CHO + 2[H] → CH₃CH₂OH.
羰基化合物的还原提供了另一条途径。用 NaBH₄ 或 LiAlH₄ 等还原剂，醛还原为伯醇，酮还原为仲醇。例如 CH₃CHO + 2[H] → CH₃CH₂OH。
6. Oxidation Reactions of Alcohols | 醇的氧化反应
Oxidation of alcohols is commonly carried out using acidified potassium dichromate(VI) solution (K₂Cr₂O₇/H₂SO₄), which turns from orange to green as Cr²⁺ ions are formed.
醇的氧化通常用酸化重铬酸钾溶液 (K₂Cr₂O₇/H₂SO₄) 进行，反应中溶液由橙色变为绿色，因为生成 Cr³⁺ 离子。
ed to a carboxylic acid: RCHO + [O] → RCOOH. To isolate the aldehyde, it must be distilled out from the reaction mixture immediately.
伯醇首先被氧化成醛：RCH₂OH + [O] → RCHO + H₂O。在过量氧化剂和加热条件下，醛进一步氧化成羧酸：RCHO + [O] → RCOOH。若要得到醛，必须立即将生成的醛从反应混合物中蒸馏出来。
nes resist further oxidation under similar conditions, so the reaction stops at the ketone stage.
仲醇被氧化成酮：R₂CHOH + [O] → R₂CO + H₂O。酮在相同条件下不易进一步氧化，因此反应停留在酮的阶段。
Tertiary alcohols do not undergo oxidation with acidified dichromate because they lack an α‑hydrogen atom necessary for the oxidation mechanism. The orange colour of the dichromate remains unchanged.
叔醇不被酸化重铬酸钾氧化，因为它们缺少氧化机理所需的 α‑氢原子。重铬酸钾的橙色保持不变。
7. Other Reactions of Alcohols: Dehydration, Halogenation and Reaction with Sodium | 醇的其他反应：脱水、卤化和与钠反应
: CH₃CH₂OH → CH₂=CH₂ + H₂O. This is an elimination reaction; unsymmetrical alcohols can produce mixtures of alkenes following Zaitsev's rule.
醇在浓硫酸加热或通过热氧化铝时发生脱水生成烯烃。乙醇生成乙烯：CH₃CH₂OH → CH₂=CH₂ + H₂O。这是消除反应；不对称醇可依据扎伊采夫规则产生烯烃混合物。
₂OH + PCl₅ → CH₃CH₂Cl + POCl₃ + HCl. This reaction is useful for laboratory preparation of chloroalkanes.
卤化反应可将羟基转化为卤原子。在室温下醇与 PCl₅ 反应生成氯代烃、POCl₃ 和 HCl：CH₃CH₂OH + PCl₅ → CH₃CH₂Cl + POCl₃ + HCl。该反应用于实验室制备氯代烃。
tion is similar to that of sodium with water but less vigorous, and the resulting alkoxide is a strong base and nucleophile.
醇还能与钠反应生成醇钠盐和氢气：2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂。该反应与钠与水的反应相似但较缓和，生成的醇钠是强碱和亲核试剂。
8. Carboxylic Acids: Acidity, Salt Formation and Esterification | 羧酸：酸性、成盐和酯化
Carboxylic acids are weak acids; in water they partially dissociate to give the carboxylate ion and H⁺: RCOOH ⇌ RCOO⁻ + H⁺. The pKₐ values are typically around 4–5, meaning they are weaker than mineral acids but stronger than alcohols and phenols.
羧酸是弱酸，在水中部分电离生成羧酸根离子和 H⁺：RCOOH ⇌ RCOO⁻ + H⁺。其 pKₐ 值通常在 4–5 左右，酸性弱于无机强酸，但强于醇和酚。
e carbon dioxide, the salt and water: CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O. This effervescence is a useful test for the carboxyl group.
羧酸与活泼金属反应放出氢气和盐：2CH₃COOH + Mg → (CH₃COO)₂Mg + H₂。与碳酸盐和碳酸氢盐反应则放出二氧化碳，生成盐和水：CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O。这种起泡现象是检验羧基的常用方法。
Esterification is a key reaction in which a carboxylic acid reacts
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