Amines

Lesson

Part 1 — derivatives of ammonia in which alkyl or aryl groups replace hydrogen.

In this lesson you will

Classify and name primary, secondary and tertiary amines and describe the amino group
Write equations for preparing amines from alcohols, alkyl halides, cyanides, amides, nitro compounds and by Gabriel synthesis
Compare boiling points of amines with each other and with alcohols
Arrange amines in order of basic strength and explain why aniline is a weak base

Table of familiar amines
Amine	Where you meet it
Trimethylamine	Smell of fish
Putrescine, cadaverine	Smell of decaying flesh
Aniline	Dyes, drugs, rubber chemicals
Adrenaline (an amine)	Hormone of “fight or flight”
Histamine	Allergic reactions

Concept

Classification and general formula

Replacing one, two or three H of NH₃ gives primary (1°) RNH₂, secondary (2°) R₂NH and tertiary (3°) R₃N amines; R₄N⁺X⁻ are quaternary ammonium salts. Saturated aliphatic amines: CₙH₂ₙ₊₃N. Aliphatic (N on alkyl C) and aromatic (N on ring C: aryl amines).

Table classifying amines
Class	Example	Formula
Primary	Propan-1-amine	CH₃CH₂CH₂NH₂
Secondary	N-Methylethanamine	CH₃CH₂NHCH₃
Tertiary	N,N-Dimethylethanamine	CH₃CH₂N(CH₃)₂
Quaternary salt	Tetramethylammonium chloride	(CH₃)₄N⁺Cl⁻
Aryl amine	Aniline (benzenamine)	C₆H₅NH₂

Diagram

Structure of the amino group

Nitrogen is sp³ with a lone pair in one hybrid orbital: amines are pyramidal, with C–N–C angles of about 108°. The lone pair makes amines bases and nucleophiles. In aniline the lone pair is partly delocalised into the ring.

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