Which of the following is `alpha-"amino"` acid ?

Options

A.
B.
C.
D. `CH_(3)-CH_(2)-underset(underset(COOH)(|))(CH)-CH_(2)-NH_(2)`

Explanation

To determine which of the given options is an alpha-amino acid, we need to understand the structure of an alpha-amino acid. An alpha-amino acid has the following characteristics:

1. It contains a carboxyl group (-COOH).
2. It has an amino group (-NH2) attached to the alpha carbon (the carbon atom that is adjacent to the carboxyl group).
3. The general structure can be represented as:
- R-CH(NH2)-COOH, where R is a side chain that varies among different amino acids.

Now, let's analyze each option step by step:

### Step 1: Identify the alpha carbon
- The alpha carbon is the carbon atom that is directly attached to the carboxyl group (-COOH).

### Step 2: Check the position of the amino group
- The amino group must be attached to the alpha carbon for the compound to be classified as an alpha-amino acid.

### Step 3: Analyze each option
- **Option A**: The amino group is located on the beta carbon (the carbon next to the alpha carbon). Therefore, this is **not** an alpha-amino acid.

- **Option B**: The amino group is attached to the alpha carbon. This fits the definition of an alpha-amino acid. Therefore, this **is** an alpha-amino acid.

- **Option C**: The amino group is located on the beta carbon. Therefore, this is **not** an alpha-amino acid.

- **Option D**: The amino group is again located on the beta carbon. Therefore, this is **not** an alpha-amino acid.

### Conclusion
After analyzing all the options, the correct answer is **Option B**, which is the alpha-amino acid.

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