A schematic analysis of the reaction of the enantiomer with racemic mixture is shows below:
`{:(d,+,"d and l",rarr,(d)-(d)),("The(+)-form of",,"A racemic mixture of",,+),("chiral molecules",,"other molecules with",,(d)-(l)),(,,50%(d) and 50%(l),,):}`
The products (d-d) and (d-l) are clearly neither identical nor enantiomers (non-superimposable mirror images) as the diastereomers, stereoisomers that are not mirror images' . The formation of diasteromers allows the separation of enantiomers (called resolution) which is not easy as enantiomers have identical physical properties. One general with naturally occurring chiral molecule to form a pair of diastereomers. These can be separated easily as they have different physical properties. If the original chemical reaction can be reversed, the enantiomers can be isolated.
Which of the following is an example of diastereomers ?

Options

A. (a) Two gauche forms of butane.
B. (b) Products of bromination of cis-2-butene in the presence of `C Cl_(4)`.
C. (c) Gauche and anti fortms of butane.
D. (d) Both (a) and (c).

Explanation

To determine which of the given options is an example of diastereomers, we need to analyze each option based on the definitions of enantiomers and diastereomers.

### Step-by-Step Solution:

1. **Understanding the Definitions**:
- **Enantiomers**: These are stereoisomers that are non-superimposable mirror images of each other.
- **Diastereomers**: These are stereoisomers that are not mirror images of each other. They have different physical properties and can be separated.

2. **Analyzing the Options**:
- **Option A: Two Gauche Forms of Butane**:
- The two gauche forms of butane are mirror images of each other.
- Therefore, they are enantiomers, not diastereomers.
- **Conclusion**: Incorrect.

- **Option B: Product of Bromination of Cystobutene in the Presence of CCl4**:
- The bromination of cystobutene produces two products that are mirror images of each other.
- Hence, these are also enantiomers.
- **Conclusion**: Incorrect.

- **Option C: Gauche and Anti Forms of Butane**:
- The gauche and anti forms of butane are not mirror images of each other.
- They have different physical properties and are therefore diastereomers.
- **Conclusion**: Correct.

- **Option D: (Assuming another example)**:
- Without specific details, we cannot analyze this option. However, if it were another pair of enantiomers, it would also be incorrect.

3. **Final Answer**:
- The correct example of diastereomers is **Option C: Gauche and Anti Forms of Butane**.