IGCSE OCR Chemistry: Aldehydes and Ketones – Key Points | IGCSE OCR 化学：醛和酮 考点精讲

📚 IGCSE OCR Chemistry: Aldehydes and Ketones – Key Points | IGCSE OCR 化学：醛和酮 考点精讲

Aldehydes and ketones are carbonyl compounds that appear prominently in the IGCSE organic chemistry syllabus. Understanding their structure, naming, preparation, characteristic reactions and the tests used to distinguish between them is essential for exam success. This revision guide covers every key point, with paired English and Chinese explanations to help you master the topic.

醛和酮是 IGCSE 有机化学大纲中出现的羰基化合物。理解它们的结构、命名、制备、特征反应以及用于区分它们的测试，对考试成功至关重要。本复习指南涵盖所有考点，并附有中英对照讲解，助你掌握该主题。

1. Introduction to Aldehydes and Ketones | 醛和酮简介

Aldehydes and ketones are important families of organic compounds that contain the carbonyl group (C=O). They are widely used as solvents, fragrances, and intermediates in chemical synthesis.

醛和酮是重要的有机化合物家族，都含有羰基 (C=O)。它们广泛用作溶剂、香料以及化学合成的中间体。

In IGCSE Chemistry, distinguishing between aldehydes and ketones and understanding their characteristic reactions are central exam topics that often appear in structured questions.

在 IGCSE 化学中，区分醛和酮并理解它们特有的反应是核心考试主题，经常出现在结构化试题中。

2. Functional Groups and General Formulas | 官能团与通式

The functional group of an aldehyde is -CHO, where the carbonyl carbon is bonded to at least one hydrogen atom. The functional group of a ketone is >C=O, where the carbonyl carbon is bonded to two carbon atoms.

醛的官能团是 -CHO，其中的羰基碳至少与一个氢原子相连。酮的官能团是 >C=O，其中的羰基碳与两个碳原子相连。

Aldehydes have the general formula CₙH₂ₙO (for saturated aldehydes), while ketones with the same number of carbons share the same general formula, making them functional group isomers. For example, propanal and propanone both have the molecular formula C₃H₆O.

醛的通式为 CₙH₂ₙO（对于饱和醛），而具有相同碳原子数的酮也具有相同的通式，因此它们互为官能团异构体。例如，丙醛和丙酮的分子式均为 C₃H₆O。

3. Naming Aldehydes and Ketones | 醛和酮的命名

For aldehydes, select the longest carbon chain containing the -CHO group, replace the ‘e’ of the corresponding alkane with ‘al’. The carbonyl carbon is always carbon 1, so no number is needed. Examples: methanal (HCHO), ethanal (CH₃CHO).

对于醛，选择含有 -CHO 基团的最长碳链，将对应烷烃的 ‘e’ 替换为 ‘al’。羰基碳始终是 1 号碳，因此不需要编号。例如：甲醛 (HCHO)、乙醛 (CH₃CHO)。

For ketones, locate the longest chain containing the carbonyl group, replace the ‘e’ with ‘one’, and number the chain so that the carbonyl carbon gets the lowest possible locant. Examples: propanone (CH₃COCH₃, no number needed as only one position), butan-2-one (CH₃COCH₂CH₃).

对于酮，找出含有羰基的最长碳链，将 ‘e’ 替换为 ‘one’，并从靠近羰基的一端给碳链编号，使羰基碳的位次尽可能小。例如：丙酮 (CH₃COCH₃，只有一个位置，无需编号)，2-丁酮 (CH₃COCH₂CH₃)。

Always provide the correct locant for ketones with 5 or more carbons, e.g., pentan-2-one, as required in exam answers.

对于含 5 个及以上碳的酮，务必在答案中给出正确的位次编号，如 2-戊酮。

4. Preparation by Oxidation of Alcohols | 通过醇氧化制备

Aldehydes are prepared by the partial oxidation of primary alcohols. Using acidified potassium dichromate(VI) (K₂Cr₂O₇/H₂SO₄), the alcohol is heated and the aldehyde is distilled off immediately to prevent further oxidation to the carboxylic acid.

醛通过伯醇的部分氧化制备。使用酸化重铬酸钾(VI) (K₂Cr₂O₇/H₂SO₄)，加热醇并立即将醛蒸馏出来，以防止进一步氧化成羧酸。

Ketones are formed by the oxidation of secondary alcohols under similar conditions; since ket

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