Aldehydes and Ketones: Key Concepts for IB & CCEA Chemistry | IB CCEA 化学：醛和酮考点精讲

📚 Aldehydes and Ketones: Key Concepts for IB & CCEA Chemistry | IB CCEA 化学：醛和酮考点精讲

Aldehydes and ketones are fundamental organic compounds containing the carbonyl functional group (C=O). In IB and CCEA Chemistry, a thorough understanding of their structure, nomenclature, reactivity, and spectroscopic identification is essential. This revision guide covers the key concepts, mechanisms, and distinguishing tests you need to master for your exams.

醛和酮是含有羰基 (C=O) 的重要有机化合物。在 IB 和 CCEA 化学课程中，深入理解它们的结构、命名、反应活性及光谱鉴定是核心考点。本复习指南涵盖了你需要掌握的关键概念、反应机理和鉴别方法，助你从容应对考试。

1. Structure and Nomenclature | 结构与命名

Both aldehydes and ketones contain a carbonyl group (C=O) but differ in the substituents attached to the carbonyl carbon. In an aldehyde, the carbonyl carbon is bonded to at least one hydrogen atom; the general formula is RCHO, where R can be H (methanal) or an alkyl/aryl group. In a ketone, the carbonyl carbon is bonded to two carbon-containing groups, with the general formula RCOR’.

醛和酮都含有羰基 (C=O)，区别在于羰基碳上连接的取代基。在醛中，羰基碳至少与一个氢原子相连；通式为 RCHO，R 可以是 H（甲醛）或烷基/芳基。在酮中，羰基碳与两个含碳基团相连，通式为 RCOR’。

IUPAC naming for aldehydes involves replacing the final ‘-e’ of the parent alkane with ‘-al’. The aldehyde group is always at carbon 1, so no number is needed for simple aldehydes. For example, CH₃CH₂CHO is propanal. When the aldehyde is attached to a ring, the suffix ‘-carbaldehyde’ is used (e.g., cyclohexanecarbaldehyde). Ketones are named by replacing ‘-e’ with ‘-one’ and a number indicates the position of the carbonyl group (e.g., CH₃COCH₂CH₃ is butan-2-one).

醛的 IUPAC 命名是将母体烷烃词尾的 ‘e’ 改为 ‘al’。醛基总是位于第一位碳，因此简单醛不需要标号。例如 CH₃CH₂CHO 为丙醛。当醛基连在环上时，使用后缀 ‘甲醛’（如环己烷甲醛）。酮的命名是将词尾 ‘e’ 改为 ‘one’，并用数字标明羰基位置（如 CH₃COCH₂CH₃ 为丁-2-酮）。

Carbonyl carbon is sp² hybridised, giving a trigonal planar geometry with bond angles of approximately 120°. The C=O bond is polar due to the higher electronegativity of oxygen, making the carbon partially positive (δ+) and susceptible to nucleophilic attack.

羰基碳为 sp² 杂化，呈平面三角形结构，键角约为 120°。由于氧的电负性更高，C=O 键具有极性，碳原子带部分正电荷 (δ+)，易受亲核试剂进攻。

2. Physical Properties | 物理性质

Short-chain aldehydes and ketones are soluble in water due to hydrogen bonding between the carbonyl oxygen and water molecules. As the hydrocarbon chain length increases, solubility decreases. They have higher boiling points than alkanes of similar molecular mass because of dipole-dipole interactions, but lower boiling points than corresponding alcohols which can form intermolecular hydrogen bonds.

短链醛和酮可溶于水，因为羰基氧能与水分子形成氢键。随着烃链增长，溶解度降低。它们的沸点高于分子量相近的烷烃，这是因为存在偶极-偶极作用，但低于相应的醇，因为醇能形成分子间氢键。

Methanal (formaldehyde) is a gas at room temperature, while other simple aldehydes and ketones are volatile liquids. Their characteristic smells are often pungent, and some are used in perfumes and flavourings.

甲醛在室温下是气体，而其他简单醛和酮是挥发性液体。它们常具有刺激性气味，有些用于香水和调味料。

3. Preparation of Aldehydes and Ketones | 醛和酮的制备

Aldehydes can be prepared by the controlled oxidation of primary alcohols using acidified potassium dichromate(VI) (K₂Cr₂O

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