Which of the following statements must be true for two pure chiral isomers

Options

A. they must be enantiomers
B. they must be diastereomers
C. they must be stereoisomers
D. they must be optically active

Answer

To determine which statements must be true for two pure chiral isomers, we need to understand the properties of chiral isomers and their behavior.

### Step-by-Step Solution:

1. **Definition of Chiral Isomers**:
Chiral isomers are compounds that have at least one chiral center (usually a carbon atom bonded to four different groups). This results in non-superimposable mirror images known as enantiomers.

2. **Optical Activity**:
Chiral compounds are optically active, meaning they can rotate plane-polarized light. This rotation can be clockwise (dextrorotatory) or counterclockwise (levorotatory). Therefore, any pure chiral isomer must exhibit optical activity.

3. **Enantiomers**:
Pure chiral isomers are often enantiomers, which are a specific type of chiral isomer. Enantiomers are pairs of chiral molecules that are mirror images of each other. However, not all chiral isomers are enantiomers; they can also exist as diastereomers if they have multiple chiral centers.

4. **Conclusion**:
The statement that must be true for two pure chiral isomers is that they are optically active. This is a defining characteristic of chiral compounds.

### Final Answer:
The statement that must be true for two pure chiral isomers is that they are optically active.

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