Which one of the following carbonyl compounds cannot be prepared by addition of water on an alkyne in the presence of `HgSO_4 and H_2 SO_4` ?

Options

A. `CH_3-overset(O)overset(||)C-H`
B.
C. `CH_3-CH_2-overset(O)overset(||)C-H`
D. `CH_3-overset(O)overset(||)C-CH_2CH_3`

Answer

To determine which carbonyl compound cannot be prepared by the addition of water on an alkyne in the presence of HgSO₄ and H₂SO₄, we need to analyze the reaction mechanism and the types of products formed.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The reaction involves the hydration of an alkyne in the presence of mercuric sulfate (HgSO₄) and sulfuric acid (H₂SO₄). This process typically leads to the formation of carbonyl compounds (ketones or aldehydes).

2. **Mechanism of Hydration**:
- The alkyne undergoes electrophilic attack by Hg²⁺, forming a mercuric alkyne complex.
- Water then attacks this complex, leading to the formation of an enol, which subsequently tautomerizes to form a carbonyl compound (ketone or aldehyde).

3. **Types of Products**:
- If the alkyne is symmetrical (e.g., 2-butyne), the product will be a ketone.
- If the alkyne is terminal (e.g., 1-butyne), the product will be an aldehyde.

4. **Identifying the Carbonyl Compounds**:
- **Ketones**: Formed from symmetrical alkynes.
- **Aldehydes**: Formed from terminal alkynes.
- The question asks which carbonyl compound cannot be formed, implying we need to find a product that is neither a ketone nor an aldehyde.

5. **Analyzing the Options**:
- If the options include compounds like ketones (RCO-R') and aldehydes (RCHO), we can conclude that these can be formed.
- However, if one of the options is a carboxylic acid (RCOOH) or any compound that is not a ketone or aldehyde, that would be the correct answer.

6. **Conclusion**:
The carbonyl compound that cannot be prepared by this method is likely a carboxylic acid or any other compound that does not fit the ketone or aldehyde category.

### Final Answer:
The carbonyl compound that cannot be prepared by the addition of water on an alkyne in the presence of HgSO₄ and H₂SO₄ is a carboxylic acid.

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