What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

Why is the carbonyl carbon attacked by nucleophiles?

It is electron deficient because oxygen pulls electron density away, leaving a partial positive charge on carbon.

Why are aldehydes more reactive than ketones toward nucleophilic addition?

They have less steric hindrance and less electron-donating alkyl stabilisation of the carbonyl carbon.

How can you chemically distinguish an aldehyde from a ketone?

Aldehydes give a positive Tollens' (silver mirror) and Fehling's test, whereas ketones do not.

What is the aldol condensation?

Carbonyl compounds with alpha-hydrogen react in base to give beta-hydroxy aldehydes or ketones, which lose water to form enones.

Why are carboxylic acids more acidic than phenols and alcohols?

The carboxylate ion is stabilised by resonance over two equivalent oxygen atoms.

How do electron-withdrawing groups affect acid strength?

They stabilise the carboxylate ion and increase acidity (e.g. trichloroacetic acid is stronger than acetic acid).

What is the Cannizzaro reaction?

Aldehydes lacking alpha-hydrogen undergo disproportionation in concentrated alkali to an alcohol and a carboxylate salt.

Name the product when a carboxylic acid reacts with an alcohol.

An ester, formed with elimination of water (esterification).

What is the HVZ reaction?

The Hell-Volhard-Zelinsky reaction, in which carboxylic acids with alpha-hydrogen are halogenated at the alpha carbon.

Why do carboxylic acids have higher boiling points than alcohols of similar mass?

They form stable hydrogen-bonded dimers, requiring more energy to separate.

Aldehydes, Ketones and Carboxylic Acids

Class 12 Chemistry · Chemistry Part II · Chapter 3

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CBSE Class 12 · Chemistry

Electrochemistry: 9 marks, biggest unit

Marks booster + cheatsheet: key concepts in 2 lines each, common traps
7 marks each: the other four units
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CBSE Class 12 · Chemistry

Unit 8 carbonyls: 8 marks, biggest unit

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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.

Extra questions & answers

Try one from this chapter

In an aldehyde, the carbonyl carbon is bonded to:

Flashcards & interactive practice