In the following the most stable conformation of n-butane is

Options

A.
B.
C.
D.

Answer

To determine the most stable conformation of n-butane, we need to analyze the different conformers based on their torsional angles and steric interactions. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the conformers of n-butane
N-butane has several conformers, which can be categorized as:
- **Anti conformer**: where the two larger groups (methyl groups) are opposite each other (180° apart).
- **Gauche conformer**: where the two larger groups are 60° apart.
- **Eclipsed conformers**: where the larger groups are aligned with each other, either fully eclipsed (0° apart) or partially eclipsed (some angle other than 0°).

### Step 2: Analyze the conformers
- **Conformer A (Gauche)**: The torsional angle is 60°. This conformation has some steric strain due to the proximity of the methyl groups.
- **Conformer B (Anti)**: The torsional angle is 180°. This conformation minimizes steric hindrance, as the bulky groups are farthest apart.
- **Conformer C (Fully Eclipsed)**: The torsional angle is 0°. This is the least stable conformation due to maximum steric hindrance between the methyl groups.
- **Conformer D (Partially Eclipsed)**: The torsional angle is greater than 0° but less than 60°. This conformation is more stable than the fully eclipsed but less stable than the anti and gauche conformers.

### Step 3: Determine the stability order
The stability of the conformers can be ranked based on their steric interactions:
1. **Anti conformer (B)**: Most stable due to minimal steric hindrance.
2. **Gauche conformer (A)**: Less stable than anti but more stable than eclipsed forms.
3. **Partially Eclipsed conformer (D)**: Less stable than gauche.
4. **Fully Eclipsed conformer (C)**: Least stable due to maximum steric strain.

### Conclusion
The most stable conformation of n-butane is the **anti conformer** (Conformer B).

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