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).

Answer

C

Explanation

Two gauche forms of butane are same.
and
But gauche and anti forms are different. So, thety are distereomers.
So the answer is (c).