Question

Which of the following pairs of compounds are enantiomers?

• A.

  

• B.

  

• C.

  

• D.

  

Hint:

Enantiomers: invert ALL chiral centres. If even one centre is same → diastereomer.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Enantiomers are a pair of optical isomers that are non-superimposable mirror images of each other. They must have at least one chiral center and lack an internal plane of symmetry.
Step 2: Detailed Explanation:
In 2,3-butanediol (the molecules shown), there are two chiral carbons.
- A meso compound has an internal plane of symmetry and is optically inactive.
- Enantiomers are mirror images that cannot be superimposed.
In Option (D):
The first structure has configurations (2R, 3S) or (2S, 3R) depending on substituents, specifically with H and OH on opposite sides (threo form).
The second structure is the exact mirror image of the first one, where the positions of H and OH at both chiral centers are reversed.
Neither molecule has a plane of symmetry (as they are threo forms), so they are a pair of enantiomers.
Other options contain meso forms or diastereomers.
Step 3: Final Answer:
Option (D) represents a pair of enantiomers.