COMEDK202510 May 2025Morning ShiftChemistryAlcohols Phenols and EthersActual
Arrange the following in the decreasing order of their pK _ a values.
Options
- AD > C > A > B
- BA > C > D > B
- CB > D > C > A
- DC>A>B>D
Correct answer
B. A > C > D > B
Step-by-step solution
The acidity of phenols is determined by the stability of the phenoxide ion formed after the loss of a proton. Electron-withdrawing groups (EWG) increase acidity (lower pK _ a ), while electron-donating groups (EDG) decrease acidity (higher pK _ a ). The substituents at the para position for the given compounds are: [A] - NH ₂ : Strong electron-donating group by resonance ( +M ). [B] - NO ₂ : Strong electron-withdrawing group by resonance ( -M ) and induction ( -I ). [C] - OCH ₃ : Electron-donating group by resonanc