1. Which of the following is an example of diastereomers? 2. Which of the following is not true?

Question

Paragraph Type

A schematic analysis of the reaction of one enantiomer with racemic mixture is shown below:

The products (d – d) and (d – l) are clearly neither identical nor enantiomers (non–superimposable mirror image) 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 molecule to form a pair of Diastereomers. These can be separated easily as they have different physical properties. If the original chemical reaction be reversed, the enantiomers can be isolated

1. Which of the following is an example of diastereomers?

(A) Two gauche forms of butane

(B) Products of bromination of cis–2–butane in the presence of CCl4

(C) Gauche and anti–form of butane

(D) Both (A) and (C)

2. Which of the following is not true?

(A) Diastereomers have different melting points and solubilities in a given solvent

(B) Diastereomers have similar chemical properties

(C) Diastereomers are optically active compounds with same or opposite sign of rotation

(D) Diastereomers differ in adsorption

Answer 1

Correct option 1. (C) , 2. (C)

Explanation:

1. Two gauche forms of butane are same

But gauche and anti-forms are different. So, they are diastereomers. So the answer is (C).

2.(a) is true, (b) is true, and (d) is true, (Adsorption is a physical property. So it is different for diastereomers.) (c) is not true.1 Diastereomers can be optically inactive, e.g., cis- 2- butene and trans are geometrical isomers and are diastereomers.