Chapter 6, Problem 6.65P

Interpretation Introduction

Interpretation:

Based on charge stability, it is be determined why the protonation of the oxygen in the $\text{C=O}$ group takes place selectively when there is another oxygen atom that can be protonated.

Concept introduction:

For a proton transfer reaction, the stability of a particular species depends on the following factors in the given order: charge, atom, resonance delocalization, and inductive effects. If protonation occurs at the same atom, then resonance delocalization effects needs to be considered. Stability of a particular structure increases as the number of atoms over which a charge is shared increases. A positive charge on a less electronegative atom is more stable than a positive charge on a more electronegative atom. In the acid catalyzed reaction of an ester, the first step in the mechanism is believed to be the protonation of the oxygen atom in the $\text{C=O}$ group. The acid catalyzed hydrolysis of an ester converts an ester into a carboxylic acid.