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Chemistry Question 70 – JEE-MAIN 2026

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Which of the following amino acid will give violet coloured complex with neutral ferric chloride solution ?

Recall the specific functional groups that react with neutral ferric chloride solution to produce colored complexes.

Step 1: Understand the Ferric Chloride Test✦ Active

The neutral ferric chloride test is a qualitative test used to detect the presence of phenolic hydroxyl groups (−OH directly attached to an aromatic ring). Phenols react with neutral ferric chloride solution to form characteristic colored complexes, often violet, blue, or green.

Step 2: Analyze Amino Acid Structures○ Expand

Examine the side chains of the given amino acids:

1. **Threonine:** Contains an aliphatic hydroxyl group (−CH(OH)CH3). This is not a phenol.

2. **Serine:** Contains an aliphatic hydroxyl group (−CH2OH). This is not a phenol.

3. **Tyrosine:** Contains a phenolic hydroxyl group (−CH2−C6H4−OH). The hydroxyl group is directly attached to a benzene ring.

4. **Cysteine:** Contains a thiol group (−CH2SH). This is neither a hydroxyl group nor a phenol.

💡 Teacher's Secret Hint

Recall the specific functional groups present in the side chains of common amino acids.

Step 3: Identify the Correct Amino Acid○ Expand

Based on the analysis, only Tyrosine possesses a phenolic hydroxyl group in its side chain. Therefore, Tyrosine will give a violet-colored complex with neutral ferric chloride solution.

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