Arrange the following conformations of ethane in the order of decreasing stability

Options

A. Eclipsed `gt` Staggered `gt` Skewed
B. Eclipsed `gt` Skewed `gt` Staggered
C. Staggered `gt` Eclipsed `gt` Skewed
D. Staggered `gt` Skewed `gt` Eclipsed

Answer

To arrange the conformations of ethane in order of decreasing stability, we need to analyze the three types of conformations: eclipsed, staggered, and skewed. Here’s a step-by-step solution:

### Step 1: Understand the Conformations of Ethane
Ethane (C2H6) can adopt different conformations due to rotation around the carbon-carbon sigma bond. The three main conformations are:
1. **Eclipsed**: The hydrogen atoms on the front and back carbons are aligned with each other (theta = 0°).
2. **Staggered**: The hydrogen atoms on the front and back carbons are staggered, maximizing the distance between them (theta = 60°).
3. **Skewed**: This conformation is between eclipsed and staggered, with a dihedral angle greater than 0° but less than 60°.

### Step 2: Analyze Stability
- **Eclipsed Conformation**: This conformation has the highest torsional strain because the hydrogen atoms overlap, leading to increased energy and decreased stability.
- **Staggered Conformation**: This is the most stable conformation as it has the least torsional strain, with maximum distance between the hydrogen atoms, resulting in lower energy.
- **Skewed Conformation**: This conformation is more stable than eclipsed but less stable than staggered. It has intermediate torsional strain.

### Step 3: Arrange in Order of Decreasing Stability
Based on the analysis:
1. **Staggered** (most stable)
2. **Skewed** (intermediate stability)
3. **Eclipsed** (least stable)

Thus, the order of decreasing stability is:
1. Staggered
2. Skewed
3. Eclipsed

### Final Answer
The correct order of decreasing stability of the conformations of ethane is:
**Staggered > Skewed > Eclipsed**

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