MCAT Organic Chemistry Question 28: Answer and Explanation
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Question: 28
13. Omeprazole is a proton pump inhibitor commonly used in gastroesophageal reflux disease. When omeprazole, a racemic mixture, went off-patent, pharmaceutical companies began to manufacture esomeprazole, the (S)-enantiomer of omeprazole, by itself. Given 1 M solutions of omeprazole and esomeprazole, which solution(s) would likely exhibit optical activity?
- A. Omeprazole only
- B. Esomeprazole only
- C. Both omeprazole and esomeprazole
- D. Neither omeprazole nor esomeprazole
Correct Answer: B
Explanation:
Racemic mixtures like omeprazole contain equimolar amounts of two enantiomers and thus have no observed optical activity. Each of the two enantiomers causes rotation in opposite directions, so their effects cancel out. Esomeprazole only contains one of the two enantiomers and thus should cause rotation of plane-polarized light.