MCAT Organic Chemistry Question 24: Answer and Explanation
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Question: 24
9. Consider (E)-2-butene and (Z)-2-butene. This is a pair of what type(s) of isomers?
I. Cis–trans isomers
II. Diastereomers
III. Enantiomers
- A. I only
- B. II only
- C. I and II only
- D. I and III only
Correct Answer: C
Explanation:
(E)-2-butene can also be called trans-2-butene; (Z)-2-butene can also be called cis-2-butene. As such, they are cis–trans isomers. Remember that cis–trans isomers are a subtype of diastereomers in which the position of substituents differs about an immovable bond. Diastereomers are molecules that are non-mirror-image stereoisomers (molecules with the same atomic connectivity). These are not enantiomers because they are not mirror images of each other.