MCAT Organic Chemistry Question 124: Answer and Explanation
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Question: 124
4. Each of the acyl compounds listed below contains a six-membered ring EXCEPT:
- A. δ-lactam.
- B. cyclohexane carboxylic acid.
- C. γ-butyrolactone.
- D. the anhydride formed from intramolecular ring closure of pentanedioic acid.
Correct Answer: C
Explanation:
This question requires knowledge of the nomenclature of cyclic molecules. A δ-lactam, choice (A), has a bond between the nitrogen and the fourth carbon away from the carbonyl carbon. This ring will have six elements: the nitrogen, the carbonyl carbon, and the four carbons in between. Cyclohexane carboxylic acid, choice (B), has cyclohexane, a six-membered cycloalkane. The anhydride formed from pentanedioic acid, choice (D), will have the five carbons in the parent chain and one oxygen atom closing the ring, meaning there are still six elements. γ-butyrolactone will have five elements because it contains a bond between the ester oxygen and the third carbon away from the carbonyl carbon. The five elements will be the oxygen, the carbonyl carbon, and the three carbons in between.