Which of the isomers of n-butyl alcohol exhibit optical isomerism ?

Options

A. Butyl alcohol
B. Sec.Butyl alcohol
C. 2-Methyl-1-propanol
D. 2-Methyl-2-Propanol

Answer

To determine which isomers of n-butyl alcohol exhibit optical isomerism, we need to identify the structures of the isomers and check for the presence of chiral centers. Here’s a step-by-step solution:

### Step 1: Identify the Isomers of n-Butyl Alcohol
n-Butyl alcohol (C4H9OH) has several structural isomers. The common isomers are:
1. **n-Butyl alcohol (1-butanol)**: CH3-CH2-CH2-CH2OH
2. **Isobutyl alcohol (2-methyl-1-propanol)**: (CH3)2CH-CH2OH
3. **Sec-butyl alcohol (2-butanol)**: CH3-CH(OH)-CH2-CH3
4. **Tert-butyl alcohol (2-methyl-2-propanol)**: (CH3)3COH

### Step 2: Determine Chiral Centers
A chiral carbon is a carbon atom that is attached to four different groups. We will analyze each isomer for chiral centers.

1. **n-Butyl alcohol (1-butanol)**:
- Structure: CH3-CH2-CH2-CH2OH
- Chiral centers: None (all carbons are bonded to at least two of the same groups).

2. **Isobutyl alcohol (2-methyl-1-propanol)**:
- Structure: (CH3)2CH-CH2OH
- Chiral centers: None (the carbon with the OH group is bonded to two methyl groups).

3. **Sec-butyl alcohol (2-butanol)**:
- Structure: CH3-CH(OH)-CH2-CH3
- Chiral centers: Yes, the carbon with the OH group is bonded to CH3, CH2, and OH, making it a chiral center.

4. **Tert-butyl alcohol (2-methyl-2-propanol)**:
- Structure: (CH3)3COH
- Chiral centers: None (the central carbon is bonded to three methyl groups).

### Step 3: Conclusion
Among the isomers of n-butyl alcohol, only **sec-butyl alcohol (2-butanol)** exhibits optical isomerism due to the presence of a chiral carbon.

### Final Answer:
**Sec-butyl alcohol (2-butanol)** is the only isomer of n-butyl alcohol that exhibits optical isomerism.

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