Most stable conformation of n-butane is :

Options

A. Gauche-form
B. Partially eclipsed form
C. Anti-form
D. Eclipsed form

Answer

To determine the most stable conformation of n-butane, we need to analyze the different conformations available and evaluate their stability based on steric strain and torsional strain.

### Step-by-Step Solution:

1. **Identify the Conformations of n-Butane:**
n-Butane can adopt several conformations, including:
- Fully eclipsed form
- Partially eclipsed form
- Staggered form (anti and gauche)

2. **Analyze the Fully Eclipsed Form:**
- In the fully eclipsed conformation, the bulky groups (methyl groups, CH3) are directly aligned with each other.
- This alignment leads to maximum steric hindrance and torsional strain due to the repulsion between the electron clouds of the overlapping bonds.
- **Conclusion:** This conformation is the least stable due to high strain.

3. **Analyze the Partially Eclipsed Form:**
- In the partially eclipsed conformation, one methyl group is eclipsed with a hydrogen atom.
- While this reduces some steric hindrance compared to the fully eclipsed form, there is still significant strain due to the proximity of the bulky groups.
- **Conclusion:** This conformation is also not very stable.

4. **Analyze the Staggered Form:**
- The staggered conformation can be further divided into:
- **Anti Conformation:** The two methyl groups are opposite each other (180 degrees apart).
- **Gauche Conformation:** The two methyl groups are 60 degrees apart.
- In the anti conformation, there is minimal steric hindrance and torsional strain, making it the most stable conformation.
- In the gauche conformation, there is some steric strain due to the proximity of the bulky groups.
- **Conclusion:** The anti conformation is the most stable due to the least strain.

5. **Final Conclusion:**
- Based on the analysis, the most stable conformation of n-butane is the **anti form** (also known as the staggered form).

### Answer:
The most stable conformation of n-butane is the **anti form** (staggered form).