Carboxylic Acids | 羧酸

📚 Carboxylic Acids | 羧酸

Carboxylic acids are a homologous series of organic compounds containing the carboxyl functional group, –COOH. In Edexcel A-Level Chemistry Topic 18.5, you must understand their structure, physical properties, acidity and reactions, including esterification and formation of acyl chlorides.

羧酸是一类含有羧基官能团（–COOH）的同系有机化合物。在爱德思 A-Level 化学 Topic 18.5 中，你需要理解它们的结构、物理性质、酸性以及反应，包括酯化和生成酰氯。

1. Structure and Nomenclature | 结构与命名

The carboxyl group –COOH consists of a carbonyl group C=O and a hydroxyl group –OH bonded to the same carbon atom. The carbon in the carboxyl group is sp² hybridised, giving a planar arrangement around that carbon.

羧基 –COOH 由羰基 C=O 和羟基 –OH 连接在同一个碳原子上组成。羧基中的碳为 sp² 杂化，使该碳周围呈平面结构。

Aliphatic carboxylic acids are named by replacing the final -e of the parent alkane with -oic acid. The carboxyl carbon is always counted as carbon 1.

脂肪族羧酸的命名是将母体烷烃词尾的 -e 改为 -oic acid。羧基碳始终编为 1 号碳。

Aromatic carboxylic acids also exist: benzoic acid is the simplest example, with the –COOH group attached directly to a benzene ring.

芳香族羧酸也存在：苯甲酸是最简单的例子，其 –COOH 直接连接在苯环上。

2. Physical Properties | 物理性质

Carboxylic acids have higher boiling points than alcohols, aldehydes and ketones of similar molar mass. This is because each carboxylic acid molecule can form two hydrogen bonds per carboxyl group, allowing the formation of hydrogen-bonded dimers.

羧酸的沸点高于相对分子质量相近的醇、醛和酮。这是因为每个羧酸分子可通过每个羧基形成两个氢键，从而形成氢键二聚体。

Short-chain carboxylic acids with up to about four carbon atoms are very soluble in water. They form hydrogen bonds with water molecules, but solubility decreases as the non-polar hydrocarbon chain becomes longer.

碳链不超过约四个碳原子的短链羧酸易溶于水。它们与水分子形成氢键，但随着非极性烃链增长，溶解度会下降。

The hydrogen-bonded dimer of ethanoic acid can be represented as two molecules held together by two C=O···H–O interactions.

乙酸的氢键二聚体可以表示为两个分子通过两个 C=O···H–O 相互作用连接在一起。

3. Acidity of Carb

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