Which will be the correct stability order of the different conformations of n - butane ?

Options

A. Fully - eclipsed `gt` eclipsed `gt` gauche `gt` anti - staggered
B. Anti - staggered `gt` eclipsed `gt` gauche `gt` fully - eclipsed
C. Anti - staggered `gt`gauche `gt` eclipsed `gt` fully - eclipsed
D. Gauche `gt` anti - staggered `gt` eclipsed `gt` fully - eclipsed

Answer

To determine the stability order of the different conformations of n-butane, we will analyze the various conformers based on steric interactions and torsional strain.

### Step-by-Step Solution:

1. **Identify the Conformations of n-butane**:
- n-butane (C4H10) has several conformations due to rotation around the C-C bonds. The main conformations include:
- Fully eclipsed
- Partially eclipsed
- Anti-staggered
- Gauche

2. **Analyze the Fully Eclipsed Conformation**:
- In the fully eclipsed conformation, the bulky groups (CH3) are directly in front of each other. This leads to significant steric hindrance and torsional strain due to the close proximity of the groups, making this conformation the least stable.

3. **Analyze the Partially Eclipsed Conformation**:
- In the partially eclipsed conformation, the bulky groups are not directly in front of each other, but there is still some overlap. This conformation is more stable than the fully eclipsed conformation but still experiences some steric repulsion.

4. **Analyze the Anti-Staggered Conformation**:
- In the anti-staggered conformation, the bulky groups (CH3) are positioned opposite each other, minimizing steric hindrance. This configuration is the most stable due to the maximum distance between the bulky groups.

5. **Analyze the Gauche Conformation**:
- In the gauche conformation, the bulky groups are adjacent to each other, which leads to some steric strain but is more stable than the fully eclipsed and partially eclipsed conformations.

6. **Establish the Stability Order**:
- Based on the analysis, the stability order of the conformations of n-butane is:
1. Anti-staggered (most stable)
2. Gauche
3. Partially eclipsed
4. Fully eclipsed (least stable)

### Final Stability Order:
- **Anti-staggered > Gauche > Partially eclipsed > Fully eclipsed**