All native α-amino acids can react with the reagents below except:

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Multiple Choice

All native α-amino acids can react with the reagents below except:

All native α‑amino acids in solution exist as zwitterions, with the amino group protonated and the carboxyl group deprotonated. Because of this, they readily form salts with acids and bases: with a strong base like NaOH, the amino group can be deprotonated and the carboxyl group stays as a salt; with an acid like HCl, the amino group becomes protonated and you obtain the corresponding acid salt. These acid–base interactions are universal for all native α‑amino acids. Ferric chloride, however, is a selective test. It reacts with compounds that have phenolic or similar electron-donating groups to form a colored complex with Fe3+. Among the standard amino acids, only tyrosine contains a phenolic OH capable of such complexation under the test conditions; most others, including glycine, lack this group and do not give a reaction with FeCl3. So not all native α‑amino acids react with ferric chloride, making that reagent the exception.

All native α‑amino acids in solution exist as zwitterions, with the amino group protonated and the carboxyl group deprotonated. Because of this, they readily form salts with acids and bases: with a strong base like NaOH, the amino group can be deprotonated and the carboxyl group stays as a salt; with an acid like HCl, the amino group becomes protonated and you obtain the corresponding acid salt. These acid–base interactions are universal for all native α‑amino acids.

Ferric chloride, however, is a selective test. It reacts with compounds that have phenolic or similar electron-donating groups to form a colored complex with Fe3+. Among the standard amino acids, only tyrosine contains a phenolic OH capable of such complexation under the test conditions; most others, including glycine, lack this group and do not give a reaction with FeCl3. So not all native α‑amino acids react with ferric chloride, making that reagent the exception.

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