Which among the following compounds is used for protection of carbonyl groups ?

Options

A. HCN
B. `CH_3OH`
C. `{:(CH_2-OH),(|),(CH_2-OH):}`
D. `C_2H_5OH`

Answer

To solve the question of which compound is used for the protection of carbonyl groups, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Carbonyl Groups**:
Carbonyl groups are functional groups characterized by a carbon atom double-bonded to an oxygen atom (C=O). They are found in aldehydes and ketones.

2. **Identifying the Need for Protection**:
In organic synthesis, it is often necessary to protect carbonyl groups to prevent them from reacting during certain chemical reactions. This is particularly important when you want to selectively reduce one carbonyl group in the presence of another.

3. **Analyzing the Options**:
The options provided are:
- a) Hydrogen cyanide (HCN)
- b) Methanol (CH3OH)
- c) Ethylene glycol (HOCH2CH2OH)
- d) Ethanol (C2H5OH)

4. **Evaluating Each Option**:
- **Hydrogen cyanide**: This is not used for protection; it is a nucleophile that can react with carbonyl groups.
- **Methanol**: While it can react with carbonyls, it is not typically used for protection.
- **Ethanol**: Similar to methanol, it can react but is not a protecting agent.
- **Ethylene glycol**: This compound can form a protective acetal with carbonyl groups, thus preventing them from undergoing further reactions.

5. **Conclusion**:
Based on the analysis, ethylene glycol (HOCH2CH2OH) is the compound used for the protection of carbonyl groups. Therefore, the correct answer is option **c) Ethylene glycol**.

### Final Answer:
**c) Ethylene glycol (HOCH2CH2OH)**

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