MCAT Organic Chemistry Question 108: Answer and Explanation

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Question: 108

3. Which of the following carboxylic acids will be the most acidic?

A. CH₃CHClCH₂COOH
B. CH₃CH₂CCl₂COOH
C. CH₃CH₂CHClCOOH
D. CH₃CH₂CH₂COOH

Correct Answer: B

Explanation:

The acidity of carboxylic acids is significantly increased by the presence of highly electronegative functional groups. Their electron-withdrawing effect increases the stability of the carboxylate anion, favoring proton dissociation. This effect increases as the number of electronegative groups on the chain increases, and it also increases as the distance between the acid functionality and electronegative group decreases. This answer has two halogens bound to it, at a smaller distance from the carboxyl group compared to the other answers.

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