Which of the following pairs of structures represents conformation isomers?

Options

A.
B.
C.
D.

Answer

To determine which pairs of structures represent conformational isomers, we need to analyze the given options based on the definitions and characteristics of conformational isomers. Conformational isomers are different spatial arrangements of the same molecule that can be interconverted by rotation around single bonds, without breaking any bonds.

### Step-by-Step Solution:

1. **Understand the Concept of Conformational Isomers**:
- Conformational isomers are different arrangements of atoms in a molecule that result from rotation around single bonds. They do not involve changes in the connectivity of the atoms.

2. **Analyze Each Option**:
- **Option A**: Check the configurations of the double bonds. If both compounds have the same configuration (E or Z) for the double bonds, they may be conformational isomers.
- **Option B**: Both double bonds in the first and second structures have the same configuration (E). This indicates that they are conformational isomers because there is no change in the configuration.
- **Option C**: Compare the configurations. If one structure has a Z configuration and the other has an E configuration, they cannot be conformational isomers as this indicates a geometrical inversion.
- **Option D**: Similar to option C, if there is a change in the configuration (like Z to E), they cannot be conformational isomers.

3. **Identify the Correct Option**:
- After analyzing all options, we find that **Option B** is the only pair that represents conformational isomers, as both structures maintain the same E configuration for the double bonds.

4. **Conclusion**:
- The correct answer is **Option B**.