Which of the following conformations of n-butane has a plane of symmetry?

Options

A.
B.
C.
D.

Answer

To determine which conformations of n-butane have a plane of symmetry, we will analyze each conformation step by step.

### Step-by-Step Solution:

1. **Understanding n-Butane Structure**:
- n-Butane (C4H10) consists of a straight chain of four carbon atoms. Each carbon is bonded to hydrogen atoms to satisfy the tetravalency of carbon.

2. **Identifying the Conformations**:
- The question provides four different conformations labeled A, B, C, and D. We will analyze each conformation to check for a plane of symmetry.

3. **Analyzing Conformation A**:
- In conformation A, we have:
- CH3 on one end, CH3 on the other end, and two hydrogen atoms in the middle.
- If we draw a plane that bisects the molecule between the two CH3 groups, we can see that each half is a mirror image of the other.
- **Conclusion**: Conformation A has a plane of symmetry.

4. **Analyzing Conformation B**:
- In conformation B, we have:
- Two hydrogen atoms on one carbon and two hydrogen atoms on the adjacent carbon.
- A plane can be drawn through the central carbon, splitting the molecule into two equal halves where each half reflects the other.
- **Conclusion**: Conformation B also has a plane of symmetry.

5. **Analyzing Conformation C**:
- In conformation C, we have:
- CH3, H, H on one side and CH3, H, H on the other side.
- There is no way to draw a plane that divides this structure into two equal halves that are mirror images of each other.
- **Conclusion**: Conformation C does not have a plane of symmetry.

6. **Analyzing Conformation D**:
- In conformation D, we have:
- CH3 on one side and CH3 on the other side, with hydrogen atoms in between.
- Similar to conformation C, there is no plane that can divide this structure into two equal halves that are mirror images.
- **Conclusion**: Conformation D does not have a plane of symmetry.

7. **Final Answer**:
- The conformations of n-butane that have a plane of symmetry are **A and B**.