JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Aldehydes Ketones and Carboxylic Acids

The correct decreasing order for acidic strength is

(A) $NO_{2} CH_{2} COOH > FCH_{2} COOH > CNCH_{2} COOH > ClCH_{2} COOH$
(B) $FCH_{2} COOH > NCCH_{2} COOH > NO_{2} CH_{2} COOH > ClCH_{2} COOH$
(C) $CNCH_{2} COOH > O_{2} NCH_{2} COOH > FCH_{2} COOH > ClCH_{2} COOH$
(D) $NO_{2} CH_{2} COOH > NCCH_{2} COOH > FCH_{2} COOH > ClCH_{2} COOH$ ✓ Correct

Answer: (D)

Solution

Acidity of these substituted acetic acids tracks how strongly the

α

-substituent pulls electron density away and so stabilises the carboxylate. The electron-withdrawing power runs

NO X_{2} > CN > F > Cl

, so the decreasing acid strength is

NO X_{2} CH X_{2} COOH > NCCH X_{2} COOH > FCH X_{2} COOH > ClCH X_{2} COOH

JEE Main · 2019 · 09 Jan 2019 · Shift 1 · Single correct option

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