Which of the following will give Hofamann alkene?

Options

A.
B.
C.
D.

Explanation

To determine which of the given reactions will yield a Hofmann alkene, we need to analyze each reaction step by step. A Hofmann alkene is characterized as a less substituted alkene that is formed during elimination reactions, particularly when a bulky base is used or when a poor leaving group is involved.

### Step-by-Step Solution:

1. **Understanding Hofmann Alkene**:
- Hofmann alkene refers to the less substituted alkene that is formed during elimination reactions. This is often the result of using a bulky base or a poor leaving group.

2. **Analyzing Reaction A (Cope Reaction)**:
- In the Cope reaction, the formation of an intermediate occurs where a nitrogen atom carries a positive charge and is surrounded by methyl groups.
- The elimination process leads to the formation of a less substituted alkene.
- **Conclusion**: Reaction A produces a Hofmann alkene.

3. **Analyzing Reaction B**:
- In this case, a bulky base is used for elimination.
- The bulky base favors the formation of the less substituted alkene by removing the leaving group and a hydrogen atom from the less hindered side.
- **Conclusion**: Reaction B also produces a Hofmann alkene.

4. **Analyzing Reaction C**:
- Here, fluorine is identified as a poor leaving group due to the strong carbon-fluorine bond.
- The elimination reaction will still favor the formation of the less substituted alkene due to the poor leaving ability of fluorine.
- **Conclusion**: Reaction C produces a Hofmann alkene as well.

5. **Analyzing Reaction D**:
- In this reaction, the elimination leads to the formation of a more substituted alkene.
- The presence of extended conjugation stabilizes the more substituted alkene, making it the preferred product.
- **Conclusion**: Reaction D does not produce a Hofmann alkene; it produces a more stable, more substituted alkene (Saytzeff product).

### Final Answer:
- The reactions that will give Hofmann alkene are **A, B, and C**. Reaction D does not yield a Hofmann alkene.