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

How are amines classified?

As primary, secondary or tertiary depending on whether one, two or three hydrogens of ammonia are replaced.

Why do amines act as bases and nucleophiles?

Nitrogen carries an unshared (lone) pair of electrons available for donation.

Why are aliphatic amines stronger bases than ammonia?

The electron-releasing alkyl groups increase electron density on nitrogen and stabilise the cation formed.

Why is aniline a weaker base than ammonia?

The nitrogen lone pair is delocalised into the benzene ring, making it less available for protonation.

Why are aromatic primary amines not prepared by the Gabriel synthesis?

Aryl halides do not undergo nucleophilic substitution with the phthalimide anion.

What is the carbylamine reaction used for?

As a test for primary amines, which give foul-smelling isocyanides with chloroform and alcoholic KOH.

How are arenediazonium salts prepared?

By treating an aromatic primary amine with nitrous acid (NaNO\(_2\)/HCl) at 273-278 K (diazotisation).

Give one replacement reaction of diazonium salts.

The Sandmeyer reaction replaces the diazo group by Cl, Br or CN using copper(I) salts.

What is a coupling reaction?

A diazonium salt couples with phenol or aniline to form a coloured azo compound used as a dye.

Why do primary amines have higher boiling points than tertiary amines of similar mass?

Primary amines form intermolecular hydrogen bonds, whereas tertiary amines cannot.

Amines

Class 12 Chemistry · Chemistry Part II · Chapter 4

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Summary

Amines are derivatives of ammonia in which one, two or three hydrogen atoms are replaced by alkyl or aryl groups, giving primary, secondary and tertiary amines respectively. The nitrogen is \(sp^3\) hybridised and pyramidal with an unshared electron pair, which makes amines behave as Lewis bases and nucleophiles. They are named by common (alkylamine) and IUPAC (alkanamine) systems. Amines are prepared by reduction of nitro compounds, nitriles and amides, by ammonolysis of alkyl halides, by the Gabriel phthalimide synthesis (for primary amines) and by the Hoffmann bromamide degradation. Primary and secondary amines form intermolecular hydrogen bonds, raising their boiling points. The basic strength of amines depends on the interplay of the inductive effect, solvation and steric hindrance; aliphatic amines are stronger bases than ammonia while aromatic amines like aniline are weaker because the nitrogen lone pair is delocalised into the ring. Amines undergo alkylation, acylation, the carbylamine test (for primary amines), reaction with nitrous acid and electrophilic substitution. Aromatic primary amines react with nitrous acid at low temperature to give diazonium salts, which are valuable intermediates: their diazo group can be replaced by halides, cyanide, hydroxyl and other groups, or retained in coupling reactions that yield azo dyes.

Structure, classification and nomenclatureMethods of preparation of aminesPhysical properties and hydrogen bondingBasic strength of aminesChemical reactions and testsDiazonium salts and their reactions

Key terms

Amine

A derivative of ammonia in which H atoms are replaced by alkyl or aryl groups; a Lewis base.

Gabriel phthalimide synthesis

A method that gives pure primary aliphatic amines from phthalimide and an alkyl halide.

Hoffmann bromamide degradation

Conversion of an amide to a primary amine with one fewer carbon using bromine and alkali.

Diazonium salt

An aryl compound of the form ArN2+ X-, a key intermediate in aromatic synthesis.

Carbylamine reaction

A test in which primary amines give foul-smelling isocyanides with chloroform and alcoholic KOH.

Coupling reaction

Reaction of a diazonium salt with phenol or arylamine to form a coloured azo dye.

Extra questions & answers

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Amines are derivatives of ammonia in which H atoms are replaced by:

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