Which of the following does not show tautomerism ?

Options

A. `C_(6) H_(5) COCH_(3)`
B. `CH_(3) CHO`
C. `CH_(3) COCH_(3)`
D. `C_(6)H_(5) COC(CH_(3))_(3)`

Answer

To determine which of the given compounds does not show tautomerism, we need to understand the concept of tautomerism, particularly keto-enol tautomerism. Tautomerism is a type of isomerism where two isomers (tautomers) can readily interconvert, typically involving the relocation of a hydrogen atom and a shift in the double bond.

### Step-by-Step Solution:

1. **Understand Tautomerism**:
- Tautomerism is primarily observed in keto-enol forms. The keto form contains a carbonyl group (C=O), while the enol form has a hydroxyl group (–OH) adjacent to a double bond (C=C).
- For tautomerism to occur, the compound must have an alpha hydrogen (a hydrogen atom attached to the carbon adjacent to the carbonyl carbon).

2. **Identify the Compounds**:
- Let's analyze each compound provided in the question to check for the presence of alpha hydrogen.

3. **Analyze Each Compound**:
- **Compound 1**: CH₆H₅C(=O)CH₃
- This compound has an alpha hydrogen on the carbon adjacent to the carbonyl group. Therefore, it can show tautomerism.
- **Compound 2**: CH₃C(=O)H
- This compound also has an alpha hydrogen. Thus, it can undergo tautomerism.
- **Compound 3**: (Another compound with a keto group)
- If this compound has an alpha hydrogen, it will also show tautomerism.
- **Compound 4**: C₆H₅C(=O)C(CH₃)₃
- In this compound, the carbonyl carbon is bonded to a carbon that does not have any alpha hydrogen (the carbon is bonded to three methyl groups). Therefore, this compound cannot undergo tautomerism.

4. **Conclusion**:
- Based on the analysis, the fourth compound does not show tautomerism because it lacks an alpha hydrogen necessary for the keto-enol interconversion.

### Final Answer:
The compound that does not show tautomerism is **Option 4**.

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