The correct order of increasing acid strength of the compounds (a) $\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}$ (b) $\mathrm{MeOCH}_{2} \mathrm{CO}_{2} \mathrm{H}$ (c) $\mathrm{CF}_{3} \mathrm{CO}_{2} \mathrm{H}$ (d) (see structure) is

JEE Main · 2006 · 30 Apr 2006 · Offline · Aldehydes Ketones and Carboxylic Acids

The correct order of increasing acid strength of the compounds
(a)

CH_{3} CO_{2} H

(b)

MeOCH_{2} CO_{2} H

(c)

CF_{3} CO_{2} H

(d) (see structure)
is

(A)b $<$ d $<$ a $<$ c
(B) $d < a < c < b$
(C)d $<$ a $<$ b $<$ c✓ Correct
(D)a $<$ d $<$ c $<$ b

Answer: (C)

Solution

Acid strength here climbs as the group attached to the carboxyl pulls electron density away and stabilises the carboxylate. Acetic acid,

C H_{3} C O_{2} H

, serves as the reference; replacing a hydrogen with a methoxy group in

MeOC H_{2} C O_{2} H

adds a mild inductive withdrawal that makes it the stronger of the two; and trifluoroacetic acid,

C F_{3} C O_{2} H

, with three fluorines exerting a powerful electron-withdrawing pull, is by far the strongest. The structure drawn as the fourth compound carries the least electron-withdrawing environment of the set and so is the weakest acid, giving an increasing order that runs from that compound to acetic acid, then methoxyacetic acid, and finally trifluoroacetic acid.

JEE Main · 2006 · 30 Apr 2006 · Offline · Single correct option

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JEE Main · 2006 · 30 Apr 2006 · Offline · Aldehydes Ketones and Carboxylic Acids

Solution

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