Question

Consider the following six compounds (A-F).

How are the two compounds in each pair related? Choose from enantiomers, epimers, diastereomers but not epimers, constitutional isomers, and identical compounds.

1. A and B
2. A and C
3. B and C
4. A and D
5. E and F

Short answer

Answer

1. Epimers
2. Enantiomers
3. Diastereomers
4. Constitutional isomers
5. Diastereomers

Step-by-step solution

Isomers

Two compounds are isomers if they have an identical chemical formula but are arranged structurally differently.

These are further classified into constitutional and stereoisomers. The two terms enantiomers and diastereomers come under stereoisomers.

Relation between two compounds for pairs a, b, and c

a. A and Bare epimers because the groups attached at C2 differ in an arrangement (H and OH are swapped).

Epimers

b. A and C are diastereomers because they are non-identical.

Enantiomers

c. B and C are enantiomers because they are mirror images of each other

Diastereomers

Relation between two compounds

d. A and D are constitutional isomers because their chemical formula is the same, but the groups are differently arranged. In A, the aldehyde is present, and in D, a ketone is present.

Constitutional isomers

e. E and F are diastereomers because the configuration is different at one or more stereocenters, and hence, they are not mirror images

Diastereomers