Which of the following structure is not meso-2,3-butanediol ?

Options

A.
B.
C.
D.

Explanation

To determine which of the given structures is not meso-2,3-butanediol, we need to analyze each structure for the presence of a plane of symmetry and the presence of chiral centers. Meso compounds have at least two chiral centers and a plane of symmetry, which makes them achiral.

### Step-by-Step Solution:

1. **Identify the Structures**: We have four structures to analyze. Let's denote them as Structure A, Structure B, Structure C, and Structure D.

2. **Analyze Structure A**:
- The structure is represented as: CH3-CHOH-CH(OH)-CH3.
- Rearranging the groups, we can visualize the structure:
- CH3 on one side, OH on the second carbon, and OH on the third carbon, with another CH3 on the opposite side.
- This structure does not have a plane of symmetry because the arrangement of the groups on the chiral centers does not mirror each other.
- **Conclusion**: Structure A is not meso-2,3-butanediol.

3. **Analyze Structure B**:
- The structure is represented similarly: CH3-CHOH-CH(OH)-CH3.
- Rearranging gives us a symmetrical arrangement with CH3 and OH groups.
- This structure has a plane of symmetry and two chiral centers.
- **Conclusion**: Structure B is meso-2,3-butanediol.

4. **Analyze Structure C**:
- The structure is again CH3-CHOH-CH(OH)-CH3.
- After rearranging, we find it has a plane of symmetry.
- It also contains two chiral centers.
- **Conclusion**: Structure C is meso-2,3-butanediol.

5. **Analyze Structure D**:
- The structure is represented as CH3-CHOH-CH(OH)-CH3.
- Rearranging shows a symmetrical arrangement.
- This structure also has a plane of symmetry and two chiral centers.
- **Conclusion**: Structure D is meso-2,3-butanediol.

6. **Final Conclusion**:
- Among the four structures, only Structure A does not exhibit the characteristics of meso-2,3-butanediol. Therefore, the answer is Structure A.