MCAT Organic Chemistry Question 22: Answer and Explanation
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Question: 22
7. The following molecules are considered to be:
- A. enantiomers.
- B. diastereomers.
- C. meso compounds.
- D. structural isomers.
Correct Answer: A
Explanation:
These compounds are nonsuperimposable mirror images. To make analysis a bit easier, we can rotate structure II 180° to look like structure III. Structures I and III more clearly have opposite stereochemistry at every chiral center, meaning that they are enantiomers.
Choice (B) is incorrect because diastereomers are stereoisomers that are not mirror images of each other. Choice (C) is incorrect because meso compounds must contain a plane of symmetry, which neither of these molecules has. Choice (D) is incorrect because structural isomers are compounds with the same molecular formula but different atomic connections. The connectivity in these two molecules is the same, which means that they are stereoisomers, not structural isomers.