Organic Chemistry MCAT Practice Exam

What distinguishes diastereomers from enantiomers?

1. Stereoisomers with at least one chiral center in common

2. Nonsuperimposable mirror images

3. Having identical properties and optical activity

4. Nonsuperimposable nonmirror images

The correct answer is: Nonsuperimposable nonmirror images

Diastereomers are defined as stereoisomers that are not mirror images of each other and cannot be superimposed, which differentiates them from enantiomers. Enantiomers are a specific type of stereoisomer that are mirror images of each other and possess opposite configurations at all chiral centers. On the other hand, diastereomers have at least one chiral center that is the same but differ in configuration at at least one other chiral center. The key characteristic of diastereomers is that they exhibit nonsuperimposable nonmirror image relationships, which means that even though they have chiral centers, their spatial arrangements do not result in them being mirror images of one another. This difference in relationship can lead to diastereomers having distinct physical and chemical properties, unlike enantiomers, which have identical physical properties except for their interaction with plane-polarized light. Thus, recognizing that diastereomers consist of stereoisomers that are nonsuperimposable nonmirror images is essential for distinguishing them from enantiomers, making the stated answer accurate.