Amines: Basicity, the Three Tests, and Aniline

In the paper

Unit 3, Organic chemistry, carries 17 of the 50 chemistry marks — the heaviest unit in the subject. With eleven chapters sharing them, this one averages a little over one and a half (MEC publishes weights by unit, not by chapter). Amines are among the two or three richest chapters in the unit: a basicity order with a reason, three distinguishing tests, and the whole of aniline chemistry.

MEC scope: Nomenclature, classification and isomerism; Preparation of primary amines; Basicity of amines; Separation of primary, secondary and tertiary amines by Hoffmann's method; Preparation and chemical properties of aniline.

Three ways it is asked:

• Recall: the reagent of the carbylamine test; what Gabriel's synthesis cannot make; the boiling point order of the amines.
• Understanding: why dimethylamine is a stronger base than trimethylamine in water but weaker in the gas phase; why aniline is a far weaker base than ethylamine; why aniline must be protected before nitration.
• Application: identify an amine from its behaviour with benzenesulphonyl chloride; predict the product of an amine with HNO₂ at 0–5 °C; count the isomeric amines of C₃H₉N.