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Chapter 3: Aldehydes, Ketones and Carboxylic Acids — Class 12 Chemistry

Chemistry · 10 chapters
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Chapter 3: Aldehydes, Ketones and Carboxylic Acids

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In an aldehyde, the carbonyl carbon is bonded to:

Summary

This unit deals with organic compounds containing the carbonyl group (>C=O) and the carboxyl group (-COOH). In aldehydes the carbonyl carbon is bonded to at least one hydrogen, in ketones it is bonded to two carbon atoms, and in carboxylic acids the carbon bears a hydroxyl as well, giving -COOH. These compounds are named by common and IUPAC systems. Aldehydes and ketones are prepared by oxidation of alcohols, ozonolysis of alkenes, hydration of alkynes and from acid derivatives; carboxylic acids are prepared by oxidation of primary alcohols and aldehydes, and from nitriles, Grignard reagents and acyl derivatives. The carbonyl carbon, being electron deficient, is attacked by nucleophiles, so aldehydes and ketones undergo nucleophilic addition reactions (with HCN, alcohols, ammonia derivatives) and the alpha-hydrogen makes them acidic enough for aldol and related condensations; aldehydes are more reactive and are readily oxidised, distinguishing them from ketones by Tollens' and Fehling's tests. Carboxylic acids are appreciably acidic because the carboxylate ion is resonance stabilised, and electron-withdrawing groups increase the acidity. They form salts, esters, anhydrides, acid chlorides and amides. These carbonyl and carboxyl compounds are constituents of perfumes, plastics, dyes, drugs and many foods.

Structure and nomenclature of carbonyl and carboxyl compoundsPreparation of aldehydes and ketonesNucleophilic addition reactionsOxidation, reduction and distinguishing testsAcidity of carboxylic acidsReactions and uses of carboxylic acids

Key terms

Carbonyl group
The >C=O group present in aldehydes and ketones, polar and electron deficient at carbon.
Nucleophilic addition
Addition of a nucleophile to the electron-deficient carbonyl carbon of aldehydes and ketones.
Aldol condensation
Reaction of carbonyl compounds bearing alpha-hydrogen to give beta-hydroxy carbonyl compounds, then enones.
Tollens' test
Reaction with ammoniacal silver nitrate giving a silver mirror, used to detect aldehydes.
Carboxyl group
The -COOH group of carboxylic acids, combining a carbonyl and a hydroxyl.
Esterification
Acid-catalysed reaction of a carboxylic acid with an alcohol to give an ester.

Important questions

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Carbonyl group
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The >C=O group present in aldehydes and ketones, polar and electron deficient at carbon.
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Practice quiz · Aldehydes, Ketones and Carboxylic Acids

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Aldehydes, Ketones and Carboxylic Acids

Chemistry 10 Qs · ~10 min