In which of the reactions, there is a migration of alkyl group to carbene `(ddot C H_2)`, i.e., rearrangement occurs ?

Options

A.
B.
C.
D.

Explanation

To determine in which reactions there is a migration of an alkyl group to a carbene, we will analyze the provided options step by step.

### Step 1: Understand the concept of carbene
A carbene is a neutral species containing a carbon atom with only six valence electrons, making it highly reactive. Carbenes can undergo rearrangements where groups attached to the carbon can migrate.

### Step 2: Analyze the reactions
We will examine each of the four options to see if they involve the formation of a carbene and if a rearrangement occurs.

#### Option A: Orn-Destert Reaction
- In this reaction, a carbene is formed.
- There is a rearrangement where an alkyl group migrates to the carbene.
- **Conclusion**: This option involves migration of an alkyl group to the carbene.

#### Option B: Wulff Rearrangement
- This reaction also leads to the formation of a carbene.
- It involves the migration of an alkyl group (or aldehyde group) to the carbene.
- **Conclusion**: This option involves migration of an alkyl group to the carbene.

#### Option C: Another Rearrangement Reaction (not specified)
- Similar to the previous two, if this reaction forms a carbene and involves rearrangement, it would also show migration.
- **Conclusion**: This option likely involves migration of an alkyl group to the carbene.

#### Option D: Hoffmann Bromamide Reaction
- This reaction does not form a carbene; instead, it leads to the formation of a nitrene.
- Since there is no carbene formation, there is no rearrangement involving migration.
- **Conclusion**: This option does NOT involve migration of an alkyl group to a carbene.

### Step 3: Final Conclusion
Based on the analysis:
- Options A, B, and C involve the migration of an alkyl group to a carbene.
- Option D does not involve carbene formation and thus does not involve migration.

### Final Answer
The reactions in which there is a migration of an alkyl group to carbene (i.e., rearrangement occurs) are **Option A, Option B, and Option C**.

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