NEET 2019 · ChemistryCarbonyl groupPrevious Year Question
The compound that is most difficult to protonate is:
Answer: (D) (D) . \textbf{Answer:} (D) (benzaldehyde).
- A.(A)
- B.(B)
- C.(C)
- D.(D) ✓
Correct Answer
(D) (D)
Solution & Explanation
\textbf{Answer:} (D) (benzaldehyde). \textbf{Solution:} Protonation occurs on the carbonyl oxygen, so the compound whose oxygen has the lowest electron density is hardest to protonate. Electron-donating () alkyl groups raise the oxygen's electron density (acetone acetaldehyde formaldehyde), making protonation easier. In benzaldehyde the phenyl ring withdraws electron density from the by conjugation, lowering the oxygen basicity, so benzaldehyde is the most difficult to protonate.
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