Question

The increasing order of acid strength of the following carboxylic acids is

• A. $CICH_2-CH_2-COOH < CICH_2COOH < NC-CH_2COOH < CHCI_2COOH $
• B. $CICH_2-COOH < NC-CH_2COOH < CICH_2CH,COOH < CHCI_2COOH $
• C. $CICH_2-CH_2-COOH < CHCI_2-COOH < CICH_2-COOH < NC-CH_2-COOH $
• D. $ NC-CH_2-COOH < CI-CH_2COOH < CH-Cl_2,COOH < CI-CH_2CH_2COOH $
• E. $CICH_2CH_2-COOH <CHCl_2,COOH < CICH_2COOH < NC-CH_2COOH $

Answer 1

The Correct Option is C

The acid strength of carboxylic acids depends on the electron-withdrawing nature of substituents near the –COOH group. Electron-withdrawing groups (EWGs) stabilize the carboxylate ion formed after losing a proton, thereby increasing acidity.

Let’s analyze the given acids: 

• \( ClCH_2CH_2COOH \): The chlorine is two carbons away, so the inductive effect is weak → least acidic
• \( CHCl_2COOH \): Has two chlorine atoms directly attached to the α-carbon → strong EWG → very acidic
• \( ClCH_2COOH \): One chlorine on α-carbon → moderate EWG → more acidic than first
• \( NCCH_2COOH \): Nitrile is a strong EWG and stabilizes the carboxylate ion effectively → most acidic

So, the increasing order of acid strength is:

\( ClCH_2CH_2COOH < CHCl_2COOH < ClCH_2COOH < NCCH_2COOH \)

Correct Answer: (C)