Which of the following pairs represents constitutional isomers?

Options

A. 2-methylbutane and pentane
B. Propyl chloride and isopropyl chloride
C. 2-chlorohexane and 3 - chlorohexane
D. All of the above

Answer

To determine which pairs represent constitutional isomers, we need to understand what constitutional isomers are. Constitutional isomers are compounds that have the same molecular formula but differ in the connectivity of their atoms. This means that while the number of each type of atom is the same, the way these atoms are bonded together is different.

### Step-by-Step Solution:

1. **Identify the pairs given in the question**:
- The pairs mentioned are 2-Methylbutane and Pentane, Propyl chloride and Isopropyl chloride, and 2-chlorohexane and 3-chlorohexane.

2. **Analyze the first pair: 2-Methylbutane and Pentane**:
- **Molecular Formula**: Both have the formula C5H12.
- **Structure**:
- 2-Methylbutane: CH3-CH(CH3)-CH2-CH3
- Pentane: CH3-CH2-CH2-CH2-CH3
- **Conclusion**: They have the same molecular formula but different structures. Therefore, they are constitutional isomers.

3. **Analyze the second pair: Propyl chloride and Isopropyl chloride**:
- **Molecular Formula**: Both have the formula C3H7Cl.
- **Structure**:
- Propyl chloride: CH3-CH2-CH2-Cl
- Isopropyl chloride: CH3-CHCl-CH3
- **Conclusion**: They have the same molecular formula but different structures. Therefore, they are constitutional isomers.

4. **Analyze the third pair: 2-chlorohexane and 3-chlorohexane**:
- **Molecular Formula**: Both have the formula C6H13Cl.
- **Structure**:
- 2-chlorohexane: CH3-CH(Cl)-CH2-CH2-CH2-CH3
- 3-chlorohexane: CH3-CH2-CH(Cl)-CH2-CH2-CH3
- **Conclusion**: They have the same molecular formula but different structures. Therefore, they are constitutional isomers.

5. **Final Conclusion**:
- All pairs mentioned (2-Methylbutane and Pentane, Propyl chloride and Isopropyl chloride, 2-chlorohexane and 3-chlorohexane) are constitutional isomers. Therefore, the correct answer is **Option 4: All of the above**.