Q65 (2026)
The correct order of acidic strength of the major products formed in the given reactions, is:
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Choose the correct answer from the options given below:
- $(1)\text{ } C > B > A > D$
- $(2)\text{ } A > D > C > B$
- $(3)\text{ } A > D > B > C$
- $(4)\text{ } C > A > D > B$
### Core Logic
Identify the major products [A], [B], [C], and [D]:
(A) $PhNH_2 \xrightarrow{1) NaNO_2 + HCl} PhN_2^+Cl^- \xrightarrow{2) CuCN} PhCN \xrightarrow{3) H_3O^+} PhCOOH$ (Benzoic acid)
(B) $CH_3CH_2CHO \xrightarrow{[Ag(NH_3)_2]^+, OH^-} CH_3CH_2COOH$ (Propanoic acid)
(C) $CH_4 + O_2 \xrightarrow{Mo_2O_3} HCHO \xrightarrow{Na_2Cr_2O_7/H^+} HCOOH$ (Formic acid)
(D) $PhCH_2MgBr + CO_2 \xrightarrow{H_3O^+} PhCH_2COOH$ (Phenylacetic acid)
### Step 1: Compare Acidity
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Acidity order: Formic acid > Benzoic acid > Phenylacetic acid > Propanoic acid.
$HCOOH$ (C) has no +I alkyl group, making it the strongest.
$PhCOOH$ (A) has an $sp^2$ carbon attached directly, which is mildly electron withdrawing via -I relative to alkyls.
$PhCH_2COOH$ (D) has an $sp^3$ methylene spacer, so -I from phenyl is weakened.
$CH_3CH_2COOH$ (B) has a purely electron-donating ethyl group (+I effect), making it the weakest.
### Step 2: Final Conclusion
Order is $C > A > D > B$.
### Pattern Recognition
$HCOOH$ is stronger than $PhCOOH$. Aliphatic acids with +I groups are the weakest.
### Evaluation Rubric / Model Answer
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### Chapter Mix
Class 12 Chemistry: Carboxylic Acids
Class 12 Chemistry: Amines
Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids
