Carboxylic acids containing an amino group `(-NH_(2))` as a substituent are called amino acids. When this amino group substitution is at `alpha` position with respect to carboxylic group, the aminoacid is called `alpha`-amino acid. The aminoacids with two carboxylic acids are called acidic amino acids whereas aminoacids with two amino group are called basic amino acids Amino acids show amphoteric character. Ali chiral natural amino acids exist in L-form. :
Each of the following represent natural alanine (an amino acid) except

Options

A.
B.
C.
D.

Answer

To solve the question regarding which structure does not represent natural alanine, we will follow these steps:

### Step 1: Understand the Structure of Alanine
Alanine is an alpha-amino acid with the following general structure:
- It has a carboxylic acid group (-COOH).
- It has an amino group (-NH2).
- The side chain (R group) for alanine is a methyl group (-CH3).

### Step 2: Identify the Configuration
Natural amino acids exist in two forms based on their spatial arrangement around the chiral carbon (the alpha carbon):
- L-form (Levorotatory)
- D-form (Dextrorotatory)

For amino acids, the L-form is typically associated with the S configuration in the Cahn-Ingold-Prelog priority rules.

### Step 3: Analyze Each Given Structure
We need to analyze the given structures of alanine to determine which one does not represent the L-form:
1. **Structure 1**: Check if the amino group (-NH2) has the highest priority, followed by the carboxylic group (-COOH), and then the hydrogen. If the hydrogen is in the back, it should be L-form.
2. **Structure 2**: Repeat the same analysis as in Structure 1.
3. **Structure 3**: Again, check the arrangement of groups around the alpha carbon.
4. **Structure 4**: This is where we need to be cautious; if the configuration leads to an R configuration instead of S, it indicates that this is not the L-form.

### Step 4: Determine the Answer
After analyzing each structure:
- If any structure leads to an R configuration, that structure does not represent natural alanine.
- The structure that results in R configuration is the answer to the question.

### Conclusion
The structure that does not represent natural alanine will be the one that is not in the L-form (i.e., has an R configuration).

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