which of the following conformations of -n- butane is least stabel ?

Options

A. Gauche
B. Anti
C. Eclipsed
D. Fully eclipsed

Answer

To determine which conformation of n-butane is the least stable, we need to analyze the different conformations of n-butane and the interactions between the substituents in each conformation.

### Step-by-Step Solution:

1. **Identify the Conformations of n-Butane**:
- n-Butane has several conformations, primarily the staggered and eclipsed forms. The main conformations we consider are:
- Staggered (anti)
- Staggered (gauche)
- Eclipsed
- Fully eclipsed

2. **Analyze the Staggered Conformations**:
- In the staggered conformation, the bulky groups (the methyl groups, -CH3) are positioned as far apart as possible, minimizing steric hindrance.
- The anti conformation (where the two methyl groups are opposite each other) is the most stable due to the maximum distance between the bulky groups.
- The gauche conformation (where the two methyl groups are adjacent) is less stable than the anti conformation but more stable than the eclipsed forms.

3. **Analyze the Eclipsed Conformations**:
- In the eclipsed conformation, the bulky groups are closer together, leading to increased steric hindrance and torsional strain.
- The eclipsed conformation is less stable than the staggered conformations due to the repulsion between the electron clouds of the overlapping bonds.

4. **Identify the Fully Eclipsed Conformation**:
- The fully eclipsed conformation has the two methyl groups directly overlapping each other. This arrangement results in the highest steric strain and torsional strain due to maximum repulsion between the electron clouds of the methyl groups.
- Thus, this conformation is the least stable among all the conformations of n-butane.

5. **Conclusion**:
- Therefore, the least stable conformation of n-butane is the **fully eclipsed conformation**.

### Final Answer:
The least stable conformation of n-butane is the **fully eclipsed conformation**.

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