In Pinacol-pinacolone rearrangement the reactive species undergoing rearrangement is

Options

A. Carbene
B. Free radical
C. Carbanion
D. Carbonium ion

Explanation

To solve the question regarding the reactive species undergoing rearrangement in the Pinacol-pinacolone rearrangement, we can break down the process step by step.

### Step-by-Step Solution:

1. **Understanding the Reaction**:
The Pinacol-pinacolone rearrangement involves the conversion of pinacol (a diol) into pinacolone (a ketone) under acidic conditions.

2. **Formation of the Carbocation**:
- The reaction begins with pinacol, which has two hydroxyl (OH) groups. In an acidic medium, one of the hydroxyl groups gets protonated, forming a good leaving group (water).
- This leads to the formation of a carbocation intermediate as the water molecule leaves.

3. **Carbocation Rearrangement**:
- The carbocation formed is typically unstable and can undergo rearrangement. In this case, a methyl group (CH3) migrates from an adjacent carbon to the positively charged carbon atom, stabilizing the carbocation.

4. **Formation of the Carbonyl Ion**:
- After the rearrangement, the new carbocation can lose a proton (H+) to form a carbonyl group (C=O), resulting in the formation of pinacolone.

5. **Identifying the Reactive Species**:
- Throughout this mechanism, the key reactive species that undergoes rearrangement is the **carbocation**. It is this carbocation that rearranges to form the final product, pinacolone.

### Final Answer:
The reactive species undergoing rearrangement in the Pinacol-pinacolone rearrangement is the **carbocation**.

---