Chapter 7, Problem 7.52P

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:

Curved arrow can be drawn from the electron-rich site to the electron-poor site to show the flow of electrons from the electron-rich site to the electron-poor site. The first curved arrow is drawn from the lone pair of the negatively charged atom of the 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 towards 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 the substrate, to which the electron-poor atom is attached. As 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 the electron-poor site to the electron-rich site and one bond is broken and another is formed simultaneously is called the proton transfer step.