2025 H2 Chem P1 Q22 — Nitrogen Compound Solution

The answer is B (1 only).
Proteins are built only from \(\alpha\)-amino acids, in which the \(\text{NH}_2\) group is on the carbon next to the \(\text{CO}_2\text{H}\) group (C-2).
• 1 is correct: 2,6-diaminohexanoic acid (lysine), \(\text{H}_2\text{N(CH}_2)_4\text{CH(NH}_2)\text{CO}_2\text{H}\), has an \(\text{NH}_2\) group on C-2, so it is an \(\alpha\)-amino acid.
• 2 is not correct: in 2-aminobenzoic acid the \(\text{NH}_2\) and \(\text{CO}_2\text{H}\) groups are both on a benzene ring, so it is not an \(\alpha\)-amino acid.
• 3 is not correct: 3-aminopropanoic acid, \(\text{H}_2\text{NCH}_2\text{CH}_2\text{CO}_2\text{H}\), has its \(\text{NH}_2\) on C-3, so it is a \(\beta\)-amino acid.
Molecules 2 and 3 can still form polyamides, but not proteins.
• A is wrong: it includes 2 and 3.
• C is wrong: it includes 2 and 3 and leaves out 1.
• D is wrong: it includes 3 and leaves out 1.