Chapter 21, Problem 21.45AP

Interpretation Introduction

(a)

Interpretation:

The base-promoted hydrolysis reaction of a thio-ester is to be compared with that of an oxygen ester. The effect of resonance stabilization of the carbonyl compound on the base-promoted hydrolysis reaction of a thio-ester and an oxygen ester is to be stated.

Concept introduction:

In oxygen esters, ester bonds are more stabilized by resonance but it’s not the same in thio-esters although the electronegativity of sulfur is less than oxygen. The thio-ester sulfur being bigger in size does not participate in resonance because overlapping of orbital is not supported.

Interpretation Introduction

(b)

Interpretation:

The effect of polar stabilization of the transition state on the base-promoted hydrolysis reaction of a thio-ester and an oxygen ester is to be stated.

Concept introduction:

The electronegativity decrease when we move down a group in periodic table. Sulfur is less electronegative than oxygen. And this is the reason sulfur shows less polarity than oxygen in molecules. Ethylthio-esters are more stable than ethyl ester because of their less polar character. Sulfur being less polar than oxygen atom, polarity in molecule is lesser and therefore transition state is more stable.