MCAT Organic Chemistry Question 47: Answer and Explanation
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Question: 47
2. Rank the following in order of decreasing nucleophilicity in an aprotic solvent: RO–, RCOOH, ROH, HO–
- A. RCOOH > ROH > RO– > HO–
- B. HO– > ROH > RO– > RCOOH
- C. RO– > HO– > ROH > RCOOH
- D. RCOOH > RO– > HO– > ROH
Correct Answer: C
Explanation:
Remember, good nucleophiles tend to have lone pairs or π bonds and are negatively charged or polarized. Alkoxide (RO–) and hydroxide (OH–) anions are strong nucleophiles. Alcohols (ROH) and carboxylic acids (RCOOH) are weak nucleophiles. The alkyl group of an alkoxide anion donates additional electron density, making it more reactive than the hydroxide ion. The carboxylic acid contains more electron-withdrawing oxygen atoms than the alcohol, making it less nucleophilic.