Which of the following reactions will undergo an elimination reaction and an alkene will be formed in the product ?

Options

A.
B.
C.
D.

Answer

To determine which of the given reactions will undergo an elimination reaction to form an alkene, we need to analyze each option based on the possibility of removing a leaving group and forming a double bond.

### Step-by-Step Solution:

1. **Understanding Elimination Reactions**:
- Elimination reactions typically involve the removal of a leaving group (like Br, OH, etc.) and a hydrogen atom from adjacent carbon atoms, resulting in the formation of a double bond (alkene).

2. **Analyzing Reaction A**:
- In reaction A, we have a compound that reacts with zinc. The zinc donates an electron, and the bromine (Br) leaves. However, the double bond that forms is on a bridgehead carbon, which leads to high angle strain due to sp² hybridization. This high strain makes the formation of the alkene unfavorable.
- **Conclusion**: Reaction A will not undergo elimination.

3. **Analyzing Reaction B**:
- In reaction B, an alcohol is present, and OH is expected to leave from a beta position. Similar to reaction A, if the double bond forms on a bridgehead carbon, it will also experience high angle strain, making the reaction unfavorable.
- **Conclusion**: Reaction B will not undergo elimination.

4. **Analyzing Reaction C**:
- In reaction C, concentrated H₂SO₄ is used, which can protonate the alcohol, leading to the formation of a carbocation. However, if the double bond forms on a bridgehead carbon, it will again lead to high angle strain, making the alkene formation unfavorable.
- **Conclusion**: Reaction C will not undergo elimination.

5. **Analyzing Reaction D**:
- In reaction D, we have N-methyl (NME) and hydroxide (OH). The hydroxide acts as a base and removes a hydrogen from the beta position. This leads to the formation of a double bond between the carbon atoms, resulting in the formation of an alkene. The elimination occurs without the formation of a bridgehead alkene, thus avoiding angle strain.
- **Conclusion**: Reaction D will undergo elimination and form an alkene.

### Final Answer:
The reaction that will undergo an elimination reaction and form an alkene is **D**.