CAIE A-Level Chemistry 34.3.3 Basicity of Amides and Amines

Practise explaining weak amide basicity through delocalisation and comparing proton-accepting ability.

Exam points

link basicity to the availability of a nitrogen lone pair to accept or coordinate to H+
delocalise the amide nitrogen lone pair into the adjacent carbonyl group, reducing its availability
rank a typical amide below ammonia below an alkylamine when the stated structures are comparable

[Maximum number: 2]

Amino acids are molecules that contain $-\mathrm{NH}_{2}$ and -COOH functional groups.
Glycine, $\mathrm{H}_{2} \mathrm{NCH}_{2} \mathrm{COOH}$ , is the simplest stable amino acid.

A student proposes a synthesis of hippuric acid by the reaction of benzamide, $\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CONH}_{2}$ , and chloroethanoic acid, $\mathrm{ClCH}_{2} \mathrm{COOH}$ .

The reaction does not work well because benzamide is a very weak base.

Explain why amides are weaker bases than amines.

M1 nitrogen lone pair in amides is delocalised with C=O

M2 lone pair less available for donation / to accept $\mathrm{H}^{+}$

OR less electron density on N / NH2 so less able to accept H ${ }^{+}$

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34.3.3—Why amides are much weaker bases than amines question 1