Question

A schematic analysis of the reaction of one enantiomer with racemic mixture is shown below
\[d+'d' \, and \, 'l'\to (d)-(d)+(d)-(l)\]

The (+) form of chiral molecules

A racemic mixture of other molecules with 50% (d) and 50% (l).

The products (d-d) and (d-l) are clearly identical or enantiomers (non-superimposable mirror images) as the mirror image of (d-d) is (l-l) not (d-l). They are diastereomers, ‘stereoisomers that are not mirror images’.
The formation of diastereomers allows the separation of enantiomers (called resolution) which is not easy as enantiomers have identical physical properties. One general procedure for separating enantiomers is to allow them to react with naturally occurring chiral molecules 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?
A. Two gauche forms of butane
B. Products of bromination of cis-2-butene in the presence of
C. Gauche and anti-forms of butane
D. Both (A) and (C)

Answer 1

Hint: Diastereomers are stereoisomers that are non-mirror images of each other, that are not identical and not superimposable on one another. These have different physical properties and also different chemical reactivity.

Complete step by step answer:
In the lower classes of chemistry, we have come across the chapter in organic chemistry named ‘stereochemistry’ which is nothing but the study of molecules in space.
Let us see this in detail and deduce the required answer.
- It is found that Gauche and anti-forms of butane are examples of diastereomers. Let’s discuss them:
- Let’s draw the gauss form firstly:

- Here, we can see that the methyl groups are present at ${{60}^{\circ }}$.
- Now let’s draw the anti-form:

- Here, we can see that in anti-form the two $C{{H}_{3}}$ groups will be on opposite sides of each other. We have to draw $C{{H}_{3}}$ at an anti position, so one$C{{H}_{3}}$ will be in an upward direction and another one will be downwards.
- Here, we can see that one is gauss form and the other is anti-form, so both are different and therefore these will be the diastereomers. So, the correct answer is “Option C”.

Note: - We should not get confused in the terms diastereomers and enantiomers. The main difference between these two is that Diastereomers have chiral centers that are non-superimposable but are not mirror images.
- Whereas, Enantiomers have chiral centers that are non-superimposable and are mirror images.