Chapter 7, Problem 7.56P

Interpretation Introduction

Interpretation:

The curved arrow notation and products for each elementary step described by the given sequence are to be drawn.

Concept introduction:

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

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.

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. Since the negatively charged anion (nucleophile) creates a bond with this carbon atom, the bond between the carbon atom and the electron-poor atom breaks. The breaking of bond and making of bond takes place simultaneously.