Which of the conformers of n - butane has maximum potential energy ?

Options

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

Answer

To determine which conformer of n-butane has the maximum potential energy, we need to analyze the different conformations that n-butane can adopt due to rotation around its carbon-carbon single bonds.

### Step-by-Step Solution:

1. **Identify the Structure of n-butane:**
- n-butane has the molecular formula C₄H₁₀ and can be represented as CH₃-CH₂-CH₂-CH₃. It consists of four carbon atoms connected by single bonds.

2. **Understand Conformational Isomerism:**
- Conformational isomers (or conformers) are different spatial arrangements of the same molecule that can be interconverted by rotation around single bonds.

3. **Draw the Newman Projections:**
- To visualize the conformers, we can use Newman projections. In these projections, we look down the bond connecting two carbon atoms (C2 and C3 in n-butane).
- The front carbon (C2) can have three groups (one CH₃ and two H) and the back carbon (C3) can also have one CH₃ and two H.

4. **Identify Key Conformers:**
- The main conformers of n-butane are:
- **Eclipsed Conformer:** When the groups on the front and back carbons are aligned (e.g., CH₃ groups are eclipsed).
- **Staggered Conformer:** When the groups are staggered (e.g., CH₃ groups are opposite each other).
- **Gauche Conformer:** When the CH₃ groups are adjacent but staggered.

5. **Analyze Potential Energy:**
- In the eclipsed conformer, the large CH₃ groups are close together, leading to significant steric hindrance and torsional strain. This results in high potential energy.
- In the staggered conformer, the groups are as far apart as possible, minimizing steric hindrance and torsional strain, resulting in lower potential energy.

6. **Conclusion:**
- The conformer of n-butane with the maximum potential energy is the **fully eclipsed conformer**. This is due to the high steric repulsion between the large CH₃ groups.

### Final Answer:
The conformer of n-butane that has maximum potential energy is the **fully eclipsed conformer**.