Question

I and II are

• A. identical
• B. a pair of conformers
• C. a pair of geometrical isomers
• D. a pair of optical isomers

Hint:

Conformers differ in spatial arrangement due to rotation around single bonds but can interconvert without breaking bonds.

Answer 1

The Correct Option is B

To analyze the relationship between structures I and II of 2,3-dibromohexane, we'll examine their stereochemical properties.

1. Structural Identification:
Both structures represent 2,3-dibromohexane with bromine atoms at the second and third carbon positions.

2. Key Considerations:
We evaluate several possibilities:
- Identical: Superimposable molecules
- Conformers: Isomers interconvertible by single bond rotation
- Geometric Isomers: Different substituent arrangements requiring bond breaking
- Optical Isomers: Non-superimposable mirror images

3. Analysis of Structures I and II:
- Both have 2 chiral centers (C2 and C3)
- The key feature is a single bond between the bromine-bearing carbons
- The structures differ only by rotation around this C-C single bond
- No bonds need to be broken to interconvert between them

4. Conclusion:
Structures I and II represent different spatial arrangements achievable through single bond rotation, making them conformers.

Final Answer:
The correct relationship is a pair of conformers (Option B).

Answer 2

Analysis: To determine the relationship between the structures I and II, we need to examine the spatial arrangement of atoms and the type of isomerism they exhibit.

Types of Isomerism:

1. Structural Isomers: Molecules with the same molecular formula but different connectivity of atoms. This is not applicable here since it's not about connectivity change but spatial arrangement.
2. Geometrical Isomers: Such isomers differ in the position of substituents around a rigid structure, like a double bond or ring. The structures here don't indicate a rigid arrangement like a double bond.
3. Optical Isomers: Molecules that are non-superimposable mirror images. Optically active compounds must have at least one chiral center. Without examining chirality or mirror images, this determination is not directly made.
4. Conformers: Also known as conformational isomers, these are forms the same compound can take by rotation around single (sigma) bonds without breaking any bonds, which is more related to flexibility due to single bonds.

Conclusion: Since structures I and II differ only in the rotation around a single bond, they are more correctly classified as a pair of conformers. This type of isomerism is due to free rotation about a single (sigma) bond, causing a different spatial arrangement.