Which is not the pair of enantiomers ?

Options

A.
B.
C.
D.

Answer

To determine which pairs of compounds are not enantiomers, we need to analyze each option and check if they are superimposable mirror images of each other. Enantiomers are pairs of molecules that are non-superimposable mirror images.

### Step-by-Step Solution:

1. **Understanding Enantiomers**:
- Enantiomers are stereoisomers that are mirror images of each other but cannot be superimposed. This means that if you place a mirror in front of one molecule, the reflection should represent the other molecule in the pair.

2. **Analyzing Each Option**:
- **Option A**:
- Molecule 1: CH3-C(Cl)(C2H5)-H
- Molecule 2: CH3-H-C(Cl)(C2H5)
- When you place a mirror, each substituent (Cl, CH3, H, C2H5) matches with its counterpart. Thus, these two are enantiomers.

- **Option B**:
- Molecule 1: COOH, H, CH3, OH
- Molecule 2: COOH, CH3, OH, H
- Again, placing a mirror shows that all groups match up correctly. Therefore, these are also enantiomers.

- **Option C**:
- Molecule 1: CH3, Br, H, C2H5
- Molecule 2: C2H5, Br, H, CH3
- Here, when you place a mirror, you notice that H is on one side and Br is on the other side, which means they cannot be superimposed. Thus, these are not enantiomers.

- **Option D**:
- Molecule 1: CHO, C2OH
- Molecule 2: C2OH, CHO
- When you place a mirror, the arrangement of groups does not match up. Therefore, these are also not enantiomers.

3. **Conclusion**:
- The pairs that are not enantiomers are **Option C** and **Option D**.

### Final Answer:
- The pairs that are not enantiomers are **Option C** and **Option D**.