Among the following the achiral amino acid is:

Options

A. 2-ethylalanine
B. 2-methylglycine
C. 2-hydroxymethylserine
D. tryptophyan.

Answer

To determine which of the given amino acids is achiral, we need to analyze the structures of each amino acid and identify whether they have a chiral center. A chiral center is typically a carbon atom that is bonded to four different groups. An achiral compound will have at least two identical groups attached to its chiral center.

### Step-by-Step Solution:

1. **Understanding Chirality**:
- A chiral molecule has a carbon atom bonded to four different substituents. An achiral molecule has at least two identical substituents on its chiral center.

2. **Analyzing 2-ethylalanine**:
- Structure: NH2-CH(CH3)-COOH with an ethyl group (C2H5) at the second position.
- Groups attached to the chiral carbon: NH2, COOH, CH3, and C2H5.
- Since all four groups are different, 2-ethylalanine is chiral.

3. **Analyzing 2-methylglycine**:
- Structure: NH2-CH(CH3)-COOH.
- Groups attached to the chiral carbon: NH2, COOH, CH3, and H.
- All four groups are different, making 2-methylglycine chiral.

4. **Analyzing 2-hydroxymethylserine**:
- Structure: HOCH2-CH(NH2)-COOH.
- Groups attached to the chiral carbon: NH2, COOH, CH2OH, and CH2OH (the two hydroxymethyl groups are identical).
- Since there are two identical groups (CH2OH), this molecule is achiral.

5. **Analyzing Tryptophan**:
- Structure: NH2-CH(C8H6N)-COOH.
- Groups attached to the chiral carbon: NH2, COOH, C8H6N (the indole group), and H.
- All four groups are different, making tryptophan chiral.

6. **Conclusion**:
- The only achiral amino acid among the options provided is **2-hydroxymethylserine**.

### Final Answer:
The achiral amino acid is **2-hydroxymethylserine**.

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