Number of conformational isomers of ethane.

Options

A. 7
B. 3
C. 4
D. Infinite

Answer

To determine the number of conformational isomers of ethane (C2H6), we need to understand the concept of conformational isomerism. Conformational isomers are different arrangements of atoms that can be interconverted by rotation around single bonds.

### Step-by-Step Solution:

1. **Identify the Structure of Ethane**:
Ethane consists of two carbon atoms connected by a single bond, with each carbon atom bonded to three hydrogen atoms. The molecular formula is C2H6.

2. **Understand Conformational Isomers**:
Conformational isomers arise due to rotation around the carbon-carbon single bond. Since the bond can rotate freely, this leads to different spatial arrangements of the atoms.

3. **Visualize the Rotation**:
When the C-C bond in ethane rotates, the hydrogen atoms can occupy different positions relative to each other. The key positions to consider are:
- **Staggered Conformation**: The hydrogen atoms on adjacent carbons are positioned as far apart as possible.
- **Eclipsed Conformation**: The hydrogen atoms on adjacent carbons are aligned with each other, leading to steric hindrance.

4. **Count the Conformational Isomers**:
- **Staggered Conformations**: There are two staggered conformations (anti and gauche).
- **Eclipsed Conformations**: There are also two eclipsed conformations (one with the hydrogen atoms directly aligned and another with the larger groups eclipsed).

5. **Total Conformational Isomers**:
Considering the rotations, we can conclude that there are infinite conformational isomers of ethane because the rotation around the C-C bond can occur continuously, leading to an infinite number of spatial arrangements.

### Conclusion:
The number of conformational isomers of ethane is infinite due to the free rotation around the carbon-carbon single bond.