Alcohol is not formed when `RMgX` is treated with

Options

A. Ethanoyl chloride
B. `O_2`
C. Oxirane
D. Methyl orthoformate

Explanation

To determine when alcohol is not formed upon treatment with Grignard reagents (RMgX), we will analyze the reactions of RMgX with the given options: ethyl chloride, O2, oxirane, and methyl orthoformate.

### Step-by-Step Solution:

1. **Understanding Grignard Reagents**:
Grignard reagents (RMgX) are highly reactive organomagnesium compounds. They act as nucleophiles and can react with various electrophiles.

2. **Analyzing Option A: Ethyl Chloride (C2H5Cl)**:
- Reaction: RMgX + C2H5Cl
- Mechanism: The R- from RMgX attacks the carbon atom of ethyl chloride, displacing the Cl- ion.
- Product: This leads to the formation of an alcohol after hydrolysis.
- Conclusion: Alcohol is formed. Therefore, this option is not the answer.

3. **Analyzing Option B: O2**:
- Reaction: RMgX + O2
- Mechanism: The R- from RMgX reacts with O2 to form a peroxide (ROO-MgX).
- Product: Upon hydrolysis, this yields an alcohol (ROH).
- Conclusion: Alcohol is formed. Therefore, this option is not the answer.

4. **Analyzing Option C: Oxirane (Epoxide)**:
- Reaction: RMgX + Oxirane
- Mechanism: The R- from RMgX attacks the less hindered carbon of the epoxide, opening the ring.
- Product: This reaction leads to the formation of an alcohol after protonation.
- Conclusion: Alcohol is formed. Therefore, this option is not the answer.

5. **Analyzing Option D: Methyl Orthoformate (HCOOCH3)**:
- Reaction: RMgX + Methyl Orthoformate
- Mechanism: The R- from RMgX attacks the carbonyl carbon of the orthoformate.
- Product: This leads to the formation of an aldehyde (H2C=O) after the reaction, without forming an alcohol.
- Conclusion: Alcohol is not formed. Therefore, this is the correct answer.

### Final Answer:
Alcohol is not formed when RMgX is treated with **methyl orthoformate (Option D)**.