Chapter 6, Problem 6.56P

Interpretation Introduction

Interpretation:

It is to be determined and explained on the basis of the pKa values which of the two electron-withdrawing groups in the substituted acetic acids $-{\text{CO}}_{\text{2}}\text{H or}-{\text{NO}}_{\text{2}}$ is stronger.

Concept introduction:

The strength of an acid is indicated by the value of its pKa. Larger the pKa, weaker the acid.

On the dissociation of the acidic proton, the stability of the anion formed decides the pKa of acid. Charge stabilization in the anion increases the strength of the acid and reduces its pKa value.

Electron-withdrawing groups move electron density away from the negatively charged atom in the anion, stabilizing the charge.