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16.1: Prelude to Aldehydes and Ketones

  • Page ID
    79316
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    The carbonyl group, \(\ce{-C=O}\), is a structural feature of many different types of compounds. It is present in carbon dioxide and in methanal, which represent respectively the high and low extremes in the level of oxidation of a carbonyl carbon:

    Roberts and Caserio Screenshot 16-0-7.png

    In between, there are carbonyl compounds ranging from aldehydes and ketones to carboxylic acids and their derivatives (esters, amides, anhydrides, and acyl halides). The naming of these compounds is described in Sections 7-4 to 7-7.

    Roberts and Caserio Screenshot 16-0-8.png

    At the upper end of the oxidation scale, along with \(\ce{CO_2}\), are the carbonic acid derivatives such as carbonic esters, amides, halides, and carbonate salts, and isocyanates:

    Roberts and Caserio Screenshot 16-0-9.png

    In this and succeeding chapters we describe the chemistry of these compounds with the intent of emphasizing the similarities that exist between them. The differences turn out to be more in degree than in kind. Even so, it is convenient to discuss aldehydes and ketones separately from carboxylic acids and, following some general observations about the carbonyl group, this chapter mainly is concerned with aldehydes and ketones.

    Apart from \(\ce{CO_2}\) and metal carbonates, the most abundant carbonyl compounds of natural origin are carboxylic esters and amides. These occur as fats and lipids, which are esters of long-chain alkanoic acids, and as proteins, which are polyamides of natural amino acids. The same structural features are found in certain synthetic polymers, in particular the polyesters (e.g., Dacron) and the polyamides (e.g., nylon 6):

    Roberts and Caserio Screenshot 16-0-10.png

    Compared to carboxylic and carbonic acid derivatives, the less highly oxidized carbonyl compounds such as aldehydes and ketones are not so widely-spread in nature. That is not to say that they are unimportant. To the contrary, aldehydes and ketones are of great importance both in biological chemistry and in synthetic organic chemistry. However, the high reactivity of the carbonyl group in these compounds enables them to function more as intermediates in metabolism or in synthesis than as end products. This fact will become evident as we discuss the chemistry of aldehydes and ketones. Especially important are the addition reactions of carbonyl groups, and this chapter is mostly concerned with this kind of reaction of aldehydes and ketones.

    Contributors and Attributions

    John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."


    This page titled 16.1: Prelude to Aldehydes and Ketones is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by John D. Roberts and Marjorie C. Caserio.