Conformations are different arrangements of atoms that are interconverted by rotation about single bond.
In eclipsed conformation, the C-H bond on-one carbon is directly aligned with C-H bond on the adjacent carbon.
In staggered conformation, the c H bond on one carbon biseçt, the H G H bond angle on adjacent carbon.
The angle that separates a bond on one atom from a bond on a adjacent atom is called a dihedral angle.
A staggered conformation with two larger groups `180^(@)` from each other is called anti. A staggered conformation with two larger group `60^(@)` from each other is called gauche.
Which of the following is gauche conformer?

Options

A.
B.
C.
D.

Explanation

To determine which of the given options represents a gauche conformer, we need to follow these steps:

### Step-by-Step Solution:

1. **Understanding Conformations**:
- Conformations are different spatial arrangements of atoms in a molecule that can be interconverted by rotation around single bonds. The two main types discussed are eclipsed and staggered conformations.

2. **Identifying Eclipsed and Staggered Conformations**:
- In an **eclipsed conformation**, the C-H bonds on one carbon are directly aligned with the C-H bonds on the adjacent carbon, creating a 0° dihedral angle.
- In a **staggered conformation**, the C-H bonds on one carbon bisect the H-H bond angle on the adjacent carbon, typically resulting in a dihedral angle of 60° or 180°.

3. **Defining Gauche and Anti Conformations**:
- A staggered conformation with two larger groups (like alkyl groups) 180° apart is referred to as **anti**.
- A staggered conformation with two larger groups 60° apart is referred to as **gauche**.

4. **Analyzing the Options**:
- We will analyze the provided options to find which one has the two larger groups (e.g., CH₃ groups) at a 60° dihedral angle.

5. **Evaluating Each Option**:
- **Option 1**: Check the angle between the larger groups. If it is 120°, it is not gauche.
- **Option 2**: Again, check the angle. If it is 180°, it is anti.
- **Option 3**: Check the angle. If it is 120°, it is not gauche.
- **Option 4**: If the angle between the larger groups is 60°, then this is the gauche conformer.

6. **Conclusion**:
- After evaluating all options, the one with the two larger groups at a 60° angle is the correct answer for the gauche conformer.

### Final Answer:
The option that represents the gauche conformer is **Option 4**.

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