MCAT Organic Chemistry Question 76: Answer and Explanation

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Question: 76

1. All of the following are true with respect to carbonyls EXCEPT:

  • A. the carbonyl carbon is electrophilic.
  • B. the carbonyl oxygen is electron-withdrawing.
  • C. a resonance structure of functional group places a positive charge on the carbonyl carbon.
  • D. the π electrons are mobile and are pulled toward the carbonyl carbon.

Correct Answer: D

Explanation:

The reactivity of the carbonyl can be attributed to the difference in electronegativity between the carbon and oxygen atoms. The more electronegative oxygen atom attracts the bonding electrons and is therefore electron-withdrawing. Thus, the carbonyl carbon is electrophilic, and the carbonyl oxygen is nucleophilic. One resonance structure of the carbonyl pushes the π electrons onto the oxygen, resulting in a positively charged carbonyl carbon.

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