Which of the following amino acids do not give purple colour on reaction with ninhydrin ?

Options

A. Proline
B. alanine
C. glycine
D. both A and B

Answer

To determine which amino acids do not give a purple color on reaction with ninhydrin, we need to understand the ninhydrin test and the structure of the amino acids involved.

### Step-by-Step Solution:

1. **Understanding Ninhydrin Test**:
- Ninhydrin is a chemical reagent used to detect amino acids. When amino acids react with ninhydrin, they typically produce a purple color, indicating the presence of free amino groups (–NH2).

2. **Identifying the Amino Acids**:
- The amino acids in question are likely to include proline, glycine, and alanine, among others. We need to analyze their structures to see if they have a free amino group.

3. **Analyzing Proline**:
- Proline is a cyclic amino acid. Its structure includes a secondary amine (–NH) instead of a primary amine (–NH2). As a result, proline does not react with ninhydrin to produce a purple color.

4. **Analyzing Glycine**:
- Glycine is the simplest amino acid with the structure NH2-CH2-COOH. It has a free amino group (–NH2) and will give a purple color with ninhydrin.

5. **Analyzing Alanine**:
- Alanine has the structure NH2-CH(CH3)-COOH. It also has a free amino group (–NH2) and will produce a purple color with ninhydrin.

6. **Conclusion**:
- Among the amino acids considered, proline is the only one that does not give a purple color when reacted with ninhydrin due to its secondary amine structure.

### Final Answer:
The amino acid that does not give a purple color on reaction with ninhydrin is **Proline**.