Question

Most acidic compound among the following is;

• A. $\text{FCH}_2\text{COOH}$
• B. $\text{CHCl}_2\text{COOH}$
• C. $\text{CH}_3\text{COOH}$
• D. $\text{C}_6\text{H}_5\text{CH}_2\text{COOH}$

Answer 1

Answer: (B)

$\text{CHCl}_2\text{COOH}$

Answer 2

Acidity of carboxylic acids is determined by the stability of their conjugate base (carboxylate ion). Electron-withdrawing groups (EWGs) stabilize the carboxylate ion by delocalizing the negative charge, thus increasing acidity. Electron-donating groups (EDGs) destabilize the carboxylate ion, decreasing acidity.

The strength of the electron-withdrawing effect depends on:

1. Electronegativity of the atom: Higher electronegativity leads to a stronger -I effect (e.g., F > Cl > Br > I).
2. Number of electron-withdrawing groups: More EWGs lead to a stronger cumulative effect.
3. Distance from the -COOH group: Closer EWGs have a stronger effect.

Comparing the options: $\text{CHCl}_2\text{COOH}$ has two chlorine atoms, resulting in a strong cumulative electron-withdrawing effect, making it the most acidic.