Which is a optically active compound ?

Options

A. Butan-2-ol
B. Isopropyl chloride
C. Neopentyl alcohol
D. Tertiary butyl alcohol

Explanation

To determine which of the given compounds is optically active, we need to identify if any of them contain a chiral carbon atom. A chiral carbon atom is one that is bonded to four different groups.

### Step-by-Step Solution:

1. **Identify the Compounds**: We have four compounds to analyze:
- Option A: Butane-2-ol
- Option B: Isopropyl chloride
- Option C: Neopentyl alcohol
- Option D: Tertiary butyl alcohol

2. **Analyze Option A: Butane-2-ol**:
- Structure: CH3-CHOH-CH2-CH3
- The second carbon (C2) has the following groups attached:
- OH (hydroxyl group)
- CH3 (methyl group)
- CH2 (ethyl group)
- H (hydrogen)
- Since C2 is attached to four different groups, it is a chiral carbon. Therefore, butane-2-ol is optically active.

3. **Analyze Option B: Isopropyl chloride**:
- Structure: (CH3)2CHOCl
- The central carbon (C2) is attached to:
- Cl (chlorine)
- CH3 (methyl group)
- CH3 (methyl group)
- H (hydrogen)
- Since C2 is attached to two identical methyl groups, it is not chiral. Thus, isopropyl chloride is not optically active.

4. **Analyze Option C: Neopentyl alcohol**:
- Structure: (CH3)4C(OH)
- The carbon with the OH group is attached to:
- OH (hydroxyl group)
- CH3 (methyl group)
- CH3 (methyl group)
- CH3 (methyl group)
- Since this carbon is attached to three identical methyl groups, it is not chiral. Therefore, neopentyl alcohol is not optically active.

5. **Analyze Option D: Tertiary butyl alcohol**:
- Structure: (CH3)3COH
- The carbon with the OH group is attached to:
- OH (hydroxyl group)
- CH3 (methyl group)
- CH3 (methyl group)
- CH3 (methyl group)
- Since this carbon is attached to three identical methyl groups, it is not chiral. Thus, tertiary butyl alcohol is not optically active.

6. **Conclusion**:
- The only compound that is optically active is **Option A: Butane-2-ol**.

### Final Answer:
**Butane-2-ol is the optically active compound.**