JEE Main 2026 Jan 28 Shift 2, Chemistry Q15: Properties of Carboxylic acids

JEE Main2026Jan 28, Shift 2Chemistry

The correct order of acidic strength of the major products formed in the given reactions, is :

A. $PhNH_{2} (1) NaNO_{2} + HCl (< 5^{\circ} C); (2) CuCN (3) H_{3} O^{+} /Δ [A]$

B. $CH_{3} CH_{2} CHO [Ag (NH_{3})_{2}]^{+}, OH^{-} /Δ [B]$

C. $CH_{4} + O_{2} (i) Mo_{2} O_{3} (ii) Na_{2} Cr_{2} O_{7} / H^{+} [C]$

D. $PhCH_{2} MgBr + CO_{2} Dry ether H_{3} O^{\oplus} [D]$

Choose the correct answer from the options given below :

A
C $>$ B $>$ A $>$ D
B
A $>$ D $>$ C $>$ B
C
A $>$ D $>$ B $>$ C
D
C $>$ A $>$ D $>$ B

Solution

Identify each major product:

A. Aniline $\to$ diazotisation $\to$ Sandmeyer with CuCN $\to$ benzonitrile $\to$ hydrolysis $\to$ benzoic acid (PhCOOH).

B. Propanal + Tollens' reagent $\to$ propanoic acid (CH $_{3}$ CH $_{2}$ COOH).

C. CH $_{4} \to$ HCHO (Mo $_{2}$ O $_{3}$ ) $\to$ further oxidation with Na $_{2}$ Cr $_{2}$ O $_{7}$ /H $^{+}$ $\to$ formic acid (HCOOH).

D. Grignard with CO $_{2}$ , then H $_{3}$ O $^{+}$ , gives phenylacetic acid (PhCH $_{2}$ COOH).

Compare $p K_{a}$ : HCOOH ( $\sim 3.75$ ) is the strongest (no alkyl +I to destabilise the anion); PhCOOH ( $\sim 4.20$ ) next (mild deactivation by ring resonance, but inductive pull from sp $^{2}$ C); PhCH $_{2}$ COOH ( $\sim 4.31$ ) next (insulating -CH $_{2}$ - weakens phenyl's effect); CH $_{3}$ CH $_{2}$ COOH ( $\sim 4.87$ ) is weakest (alkyl +I destabilises the carboxylate).

$∴$ C $>$ A $>$ D $>$ B.

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JEE Main 2026 Jan 28 Shift 2, Chemistry Q15: Properties of Carboxylic acids

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