A level Chemistry · Edexcel 9CH0 · Topic 18B
Amines, amides, amino acids and proteins
Key points
- Amines are bases because the N lone pair accepts a proton. Aliphatic amines are stronger bases than ammonia; phenylamine is weaker because the lone pair is delocalised into the ring.
- Preparation: halogenoalkane + excess ethanolic ammonia, or reduce a nitrile (LiAlH₄); phenylamine from nitrobenzene with tin and conc. HCl.
- Amines react with acids to form salts, with acyl chlorides to form amides, and with Cu²⁺(aq) to form deep blue complexes.
- Polyamides form by condensation of a diamine with a dicarboxylic acid (or diacyl chloride), e.g. nylon.
- Amino acids have NH₂ and COOH groups; in solution they form zwitterions; they are chiral (except glycine).
- Peptide bonds link amino acids into proteins; acid hydrolysis breaks them and the amino acids can be separated by chromatography.
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Nitrogen's lone pair is the key to this sub-topic. It makes amines bases and nucleophiles, and the same chemistry links amines to amides, nylon and Kevlar, and the amino acids that build every protein.
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