How many gauche conformations are possible for n-butane?

Options

A. 2
B. 3
C. 4
D. 1

Answer

To determine how many gauche conformations are possible for n-butane, we can follow these steps:

### Step 1: Understand the Structure of n-Butane
n-Butane has the molecular formula C4H10 and consists of a straight chain of four carbon atoms. The structure can be represented as:
- CH3-CH2-CH2-CH3

### Step 2: Identify the Conformational Isomers
Conformational isomers (or conformers) are different spatial arrangements of the same molecule that can be interconverted by rotation around single bonds. For n-butane, we focus on the conformations around the C2-C3 bond.

### Step 3: Analyze the Possible Conformations
When considering the rotation around the C2-C3 bond, there are several key conformations:
1. **Anti conformation** (staggered): The two methyl groups (CH3) are opposite each other (180° apart).
2. **Gauche conformations** (staggered): The two methyl groups are adjacent to each other (60° apart).
3. **Eclipsed conformations**: The methyl groups are aligned with each other (0° or 120° apart).

### Step 4: Count the Gauche Conformations
For n-butane, there are two distinct gauche conformations:
1. **Gauche 1**: Methyl groups are 60° apart.
2. **Gauche 2**: Methyl groups are 300° apart (which is equivalent to -60°).

### Step 5: Conclusion
Thus, the total number of gauche conformations for n-butane is **2**.

### Final Answer
The number of gauche conformations possible for n-butane is **2**.

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