Chapter 7, Problem 7.49P

Interpretation Introduction

(a)

Interpretation:

The electron-rich sites and electron-poor sites in the given elementary steps are to be identified.

Concept introduction:

An atom with partial or full negative charge is an electron-rich site whereas an atom with partial or full positive charge is an electron-poor site. In an elementary step, electrons tend to flow from an electron-rich site to an electron-poor site.

Interpretation Introduction

(b)

Interpretation:

In each of the given elementary steps the appropriate curved arrows are to be drawn.

Concept introduction:

The curved arrow is drawn from an electron rich site to an electron poor site to show the flow of electrons from electron-rich site to electron-poor site. The first curved arrow is drawn from the lone pair of negatively charged atom of electron-rich site to the less electronegative atom of the electron-poor site. The second curved arrow is drawn from the region between the less electronegative atom and more electronegative atom toward the more electronegative atom indicating the breaking of the bond.

Interpretation Introduction

(c)

Interpretation:

The names of each elementary step are to be identified.

Concept introduction:

In the bimolecular substitution reaction ${\text{S}}_{\text{N}}\text{2}$, electron pair from the electron-rich site approaches the carbon atom of substrate to which the electron-poor atom is attached. As the anion (nucleophile) forms a bond with this carbon atom, the bond between the carbon atom and the electron-poor atom breaks. The making and breaking of bonds takes place simultaneously.

An elementary step in which a proton is transferred from electron-poor site to electron- rich site and one bond is broken and another is formed simultaneously is called proton transfer step.