The correct sequence of acidic strength of the following aliphatic acids in their decreasing order is : $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}, \mathrm{CH}_{3} \mathrm{COOH}, \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}$, HCOOH

(A) $\mathrm{HCOOH}>\mathrm{CH}_{3} \mathrm{COOH}>\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}> \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}$

(B) $\mathrm{HCOOH}>\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}> \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}>\mathrm{CH}_{3} \mathrm{COOH}$

(C) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}>\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}> \mathrm{CH}_{3} \mathrm{COOH}>\mathrm{HCOOH}$

(D) $\mathrm{CH}_{3} \mathrm{COOH}>\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}> \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{COOH}>\mathrm{HCOOH}$

JEE Main · 2024 · 08 Apr 2024 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

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The correct sequence of acidic strength of the following aliphatic acids in their decreasing order is :

CH_{3} CH_{2} COOH, CH_{3} COOH, CH_{3} CH_{2} CH_{2} COOH

, HCOOH

(A) $HCOOH > CH_{3} COOH > CH_{3} CH_{2} COOH > CH_{3} CH_{2} CH_{2} COOH$ ✓ Correct
(B) $HCOOH > CH_{3} CH_{2} CH_{2} COOH > CH_{3} CH_{2} COOH > CH_{3} COOH$
(C) $CH_{3} CH_{2} CH_{2} COOH > CH_{3} CH_{2} COOH > CH_{3} COOH > HCOOH$
(D) $CH_{3} COOH > CH_{3} CH_{2} COOH > CH_{3} CH_{2} CH_{2} COOH > HCOOH$

Answer: (A)

Solution

Acid strength falls as the electron-donating alkyl chain lengthens (more +I effect destabilises the carboxylate) and rises sharply for formic acid, which has no alkyl group at all:

H C O O H > C H_{3} C O O H > C H_{3} C H_{2} C O O H > C H_{3} C H_{2} C H_{2} C O O H

JEE Main · 2024 · 08 Apr 2024 · Shift 2 · Single correct option

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JEE Main · 2024 · 08 Apr 2024 · Shift 2 · Aldehydes Ketones and Carboxylic Acids

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