Which of the following conformations of meso 2,3-dibromobutane will give bromoalkene with alcoholic KOH ?

Options

A. Gauche form
B. Anti form
C. Partial eclipsed form
D. Fully eclipsed form

Explanation

To determine which conformation of meso-2,3-dibromobutane will yield a bromoalkene when treated with alcoholic KOH, we need to analyze the different conformations of the compound and how they interact with the elimination reaction.

### Step-by-Step Solution:

1. **Identify the Structure of Meso-2,3-Dibromobutane**:
- Meso-2,3-dibromobutane has two bromine atoms attached to the second and third carbon atoms of a butane chain. The structure can be represented as:
```
CH3-CH(Br)-CH(Br)-CH3
```
- In a Fischer projection, this can be represented as:
```
CH3 Br
| |
Br-CH-CH3
| |
H H
```

2. **Convert to Newman Projection**:
- To analyze the conformations, we can convert the Fischer projection into Newman projections. The relevant conformations to consider are:
- Gauche form
- Anti form
- Partial eclipsed form
- Fully eclipsed form

3. **Analyze Each Conformation**:
- **Fully Eclipsed Form**: In this form, the bromine atoms and hydrogen atoms are aligned. This conformation is sterically hindered and does not favor elimination.
- **Partial Eclipsed Form**: Similar to the fully eclipsed form, this conformation also does not allow for the required anti elimination of HBr.
- **Anti Form**: In this conformation, the bromine atoms are opposite each other, but the hydrogen atoms are not in the correct orientation for elimination.
- **Gauche Form**: In this conformation, one bromine atom is adjacent to a hydrogen atom, allowing for an anti elimination mechanism. This is the most favorable conformation for elimination to occur.

4. **Elimination Reaction**:
- When treated with alcoholic KOH, the base will abstract a hydrogen atom that is anti to the bromine atom. In the Gauche form, the hydrogen and bromine are positioned correctly to allow for the elimination of HBr, leading to the formation of a bromoalkene.

5. **Conclusion**:
- The Gauche conformation of meso-2,3-dibromobutane will give the bromoalkene when treated with alcoholic KOH.

### Final Answer:
The correct answer is the **Gauche form** of meso-2,3-dibromobutane.