MCAT Organic Chemistry Question 60: Answer and Explanation
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Question: 60
15. Which conversion between carboxylic acid derivatives is NOT possible by nucleophilic reaction?
- A. Carboxylic acid to ester
- B. Ester to carboxylic acid
- C. Anhydride to amide
- D. Ester to anhydride
Correct Answer: D
Explanation:
Remember, there is a hierarchy to the reactivity of carboxylic acid derivatives that dictates how reactive they are toward nucleophilic attack. In order from highest to lowest, this is anhydrides > carboxylic acids and esters > amides. In practical terms, this means that derivatives of higher reactivity can form derivatives of lower reactivity but not vice-versa. Nucleophilic attack of an ester cannot result in the corresponding anhydride because anhydrides are more reactive than esters.