Chapter 7, Problem 7.48P

Interpretation Introduction

(a)

Interpretation:

For each step of the given reaction, which converts an epoxide into a bromohydrin, all electron-rich sites and electron-poor sites are to be identified.

Concept introduction:

An atom with partial or full negative charge is called an electron-rich site whereas an atom with partial or full positive charge is called an electron-poor site. An electron-rich atom has a lone pair of electrons whereas an electron-poor atom lacks an octet. In an elementary step, electrons tend to flow from an electron-rich site to an electron-poor site.

Interpretation Introduction

(b)

Interpretation:

Appropriate curved arrows are to be drawn to show the bond formation and bond breaking that occur in each step of the given reaction, which converts an epoxide into a bromohydrin.

Concept introduction:

In an elementary step, electrons tend to flow from an electron-rich site to an electron-poor site. One curved arrow is drawn from the lone pair of the electron-rich atom to the H attached to the electron-poor site to show the formation of a bond. A second curved arrow is drawn starting from the middle of the broken bond to the atom on which the lone pair ends up to indicate the breaking of the bond.

Interpretation Introduction

(c)

Interpretation:

Each step of the given reaction, which converts an epoxide into a bromohydrin, is to be named.

Concept introduction:

An elementary step in which a proton is transferred from an electron-poor site to an electron-rich site and one bond is broken and another is formed simultaneously is called the proton transfer step. In the ${\text{S}}_{\text{N}}\text{2}$ type of reaction, the lone pair of electrons from the electron-rich site approaches the carbon atom of the substrate to which the electron-poor atom is attached. Since the negatively charged atom (nucleophile) starts forming a bond with this carbon atom, the bond between the electron poor atom and carbon atom breaks. The making and breaking of bonds take place simultaneously.