Question

Which of the following are pair of diastereomers?

• A. (I) and (III)
• B. (II) and (IV)
• C. (I) and (II)
• D. None

Answer 1

The correct option is C (I) and (II)

The Fischer projection of (I) and (II) is wrong because the functional groups is not the top. On rotating (I) and (II) by ${180}^{\circ }$, they are represented as shown:
(I) and (III) are enantiomers as they are non-superimposable mirror image.
Also, The given compound has two chiral centre
If two compound have different absolute configuration in both chiral centre then they were related by enantiomerism

(II) and (IV) are identical or same.
If two compound have same absolute configuration at one chiral centre and different absolute configuration at another chiral centre, then, they are related by diastereomerism.
Therefore, the pairs of diastereomers are:
(I), (II); (I), (IV); and (II), (III).
But the answer given is (C) (I, II).