Which of the following shows optical isomerism?

Options

A. Butan-1-ol
B. Butan-2-ol
C. Butene
D. But-2-enol

Answer

To determine which of the given compounds shows optical isomerism, we need to identify if any of the compounds have a chiral center. A chiral center is typically a carbon atom that is bonded to four different groups. Here’s a step-by-step solution:

### Step 1: Identify the Compounds
Let's assume we have the following compounds based on the context provided:
1. Butan-1-ol
2. Butan-2-ol
3. Butan-3-ol
4. Butan-2-ene

### Step 2: Analyze Each Compound for Chirality
- **Butan-1-ol (CH3-CH2-CH2-CH2OH)**:
- The carbon atoms in this compound do not have four different substituents. The first carbon (C1) has three hydrogens and one hydroxyl group (OH), making it achiral.
- **Conclusion**: Does not show optical isomerism.

- **Butan-2-ol (CH3-CH(OH)-CH2-CH3)**:
- The second carbon (C2) is bonded to four different groups: a methyl group (CH3), a hydroxyl group (OH), an ethyl group (CH2-CH3), and a hydrogen atom (H).
- **Conclusion**: This compound has a chiral center and can show optical isomerism.

- **Butan-3-ol (CH3-CH2-CH(OH)-CH3)**:
- The third carbon (C3) is also bonded to four different groups: a hydroxyl group (OH), a methyl group (CH3), an ethyl group (CH2-CH3), and a hydrogen atom (H).
- **Conclusion**: This compound also has a chiral center and can show optical isomerism.

- **Butan-2-ene (CH3-CH=CH-CH3)**:
- The double bond between C2 and C3 means that these carbons cannot be chiral centers because they do not have four different substituents.
- **Conclusion**: Does not show optical isomerism.

### Step 3: Final Conclusion
From the analysis, **Butan-2-ol** and **Butan-3-ol** show optical isomerism due to the presence of chiral centers.

### Summary
- **Butan-1-ol**: No optical isomerism
- **Butan-2-ol**: Shows optical isomerism
- **Butan-3-ol**: Shows optical isomerism
- **Butan-2-ene**: No optical isomerism