Which of the following `alpha`-amino acids does not contain a chiral carbon ?

Options

A. Glycine
B. Alanine
C. Phenylalanine
D. valine

Answer

To determine which of the following alpha-amino acids does not contain a chiral carbon, we need to analyze the structures of the amino acids in question. A chiral carbon is defined as a carbon atom that is bonded to four different substituents.

### Step-by-Step Solution:

1. **Understand the Definition of Chiral Carbon**:
- A chiral carbon has four different groups attached to it. If any two groups are the same, the carbon is not chiral.

2. **Analyze Glycine**:
- Structure: Glycine (NH2-CH2-COOH)
- The central carbon (C) in Glycine is attached to:
- NH2 (amino group)
- COOH (carboxylic acid group)
- CH2 (hydrogen)
- H (hydrogen)
- Since there are two hydrogen atoms attached to the central carbon, Glycine does not have a chiral carbon.

3. **Analyze Alanine**:
- Structure: Alanine (NH2-CH(CH3)-COOH)
- The central carbon in Alanine is attached to:
- NH2 (amino group)
- COOH (carboxylic acid group)
- CH3 (methyl group)
- H (hydrogen)
- All four groups are different, so Alanine has a chiral carbon.

4. **Analyze Phenylalanine**:
- Structure: Phenylalanine (NH2-CH(CH2-C6H5)-COOH)
- The central carbon in Phenylalanine is attached to:
- NH2 (amino group)
- COOH (carboxylic acid group)
- CH2-C6H5 (phenyl group)
- H (hydrogen)
- All four groups are different, so Phenylalanine has a chiral carbon.

5. **Analyze Valine**:
- Structure: Valine (NH2-CH(CH(CH3)2)-COOH)
- The central carbon in Valine is attached to:
- NH2 (amino group)
- COOH (carboxylic acid group)
- CH(CH3)2 (isopropyl group)
- H (hydrogen)
- All four groups are different, so Valine has a chiral carbon.

6. **Conclusion**:
- Among the amino acids analyzed, only Glycine does not have a chiral carbon. Therefore, the answer is Glycine.

### Final Answer:
**Glycine does not contain a chiral carbon.**

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