For the given compounds, the correct order of increasing $\mathrm{pK}_{\mathrm{a}}$ value : (A) (see structure) (B) (see structure) (C) (see structure) (D) (see structure) (E) (see structure)

(A) (E) $<$ (D) $<$ (C) $<$ (B) $<$ (A)

(B) (D) $<$ (E) $<$ (C) $<$ (B) $<$ (A)

(C) (E) $<$ (D) $<$ (B) $<$ (A) $<$ (C)

(D) (B) $<$ (D) $<$ (A) $<$ (C) $<$ (E)

JEE Main · 2024 · 09 Apr 2024 · Shift 1 · Alcohols Phenols and Ethers

For the given compounds, the correct order of increasing

pK_{a}

value :
(A) (see structure)
(B) (see structure)
(C) (see structure)
(D) (see structure)
(E) (see structure)

(A)(E) $<$ (D) $<$ (C) $<$ (B) $<$ (A)
(B)(D) $<$ (E) $<$ (C) $<$ (B) $<$ (A)
(C)(E) $<$ (D) $<$ (B) $<$ (A) $<$ (C)
(D)(B) $<$ (D) $<$ (A) $<$ (C) $<$ (E)

Solution

The acidity of phenols is influenced by substituents on the benzene ring:

Electron-withdrawing groups (EWG) increase acidity by stabilizing the phenoxide ion through resonance and inductive effects. The stronger the EWG and the closer it is to the -OH group, the more acidic the phenol.

Electron-donating groups (EDG) decrease acidity by destabilizing the phenoxide ion.

(A) Phenol - baseline acidity
(B) p-nitrophenol -

NO_{2}

at para position (strong EWG, resonance + inductive)
(C) m-methoxyphenol -

OCH_{3}

at meta position (weak EDG, only inductive withdrawal at meta)
(D) m-nitrophenol -

NO_{2}

at meta position (strong EWG, only inductive)
(E) p-methoxyphenol -

OCH_{3}

at para position (EDG, resonance donation)

Acidity order: B > D > C > A > E (most acidic to least acidic)

pKₐ order (inverse of acidity): B < D < C < A < E

The correct answer should be B < D < C < A < E, which is not among the given options. The question is marked as BONUS by NTA.

JEE Main · 2024 · 09 Apr 2024 · Shift 1 · Single correct option

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JEE Main · 2024 · 09 Apr 2024 · Shift 1 · Alcohols Phenols and Ethers

Solution

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