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 determine which compound is used for the protection of carbonyl groups, we can analyze the provided options and their behavior when reacted with carbonyl compounds. Here’s a step-by-step solution:

**Step 1: Understanding the concept of protecting groups**
- Protecting groups are used in organic synthesis to temporarily mask a functional group, allowing for selective reactions without interference from the masked group.

**Hint:** Remember that protecting groups should not react under the conditions used for the desired reaction.

**Step 2: Identify the options given**
- The question provides four compounds. We need to evaluate each one to see if they can act as a protecting group for carbonyls.

**Hint:** List out the compounds you are given and prepare to analyze each one.

**Step 3: Analyze the first compound (HCN)**
- When HCN reacts with a carbonyl group, it undergoes a nucleophilic addition reaction, forming a cyanohydrin. This means HCN does not protect the carbonyl group.

**Hint:** A protecting group should not react with the carbonyl; it should form a stable compound instead.

**Step 4: Analyze the second compound (Methanol)**
- Methanol can react with carbonyls in the presence of acid to form hemiacetals. However, hemiacetals are in equilibrium with the original carbonyl compound, which means they cannot act as protecting groups.

**Hint:** Check if the product formed is stable or if it can revert back to the original functional group.

**Step 5: Analyze the third compound (Glycol)**
- Glycols can react with carbonyls to form acetals when treated with acid. Acetals are stable and do not revert back to carbonyls under normal conditions, making them effective protecting groups.

**Hint:** Look for compounds that form stable products that do not revert back to the original functional group.

**Step 6: Analyze the fourth compound (Ethanol)**
- Similar to methanol, ethanol can also form hemiacetals with carbonyls. Since hemiacetals are in equilibrium with the carbonyls, they cannot serve as protecting groups.

**Hint:** Remember that only stable products that do not revert to the original carbonyl can be considered protecting groups.

**Step 7: Conclusion**
- Based on the analysis, the compound that acts as a protecting group for carbonyl groups is the third option, which is glycol, as it forms acetals that are stable and do not revert back to the carbonyl group.

**Final Answer:** The compound used for the protection of carbonyl groups is **Glycol** (option 3).

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