Chapter 25, Problem 25.51P

Interpretation Introduction

(a)

Interpretation:

This addition of $\text{HBr}$ to $\left(\text{Z}\right)\text{-2-bromobut-2-ene}$ take place regioselectively, with the $\text{Br}$ preferentially adding to the alkene $\text{C}$ that does not already possess a $\text{Br}$ atom. A detailed mechanism for this reaction, including initiation and propagation steps is to be provided.

Concept introduction:

A free radical chain reaction involves free radicals in a cyclic sequence of steps, called propagation steps, which are responsible for converting overall reactants into overall products. Throughout the sequence of propagation steps, also called the propagation cycle, there is no net consumption of free radicals. The overall reaction is obtained by summing just the propagation steps. An initiation step is responsible for producing the free radical that enters the propagation cycle. A termination step removes free radicals from the propagation cycle and is responsible for slowing the overall reaction.

Interpretation Introduction

(b)

Interpretation:

The reason for this observed regiochemistry in the given reaction is to be explained.

Concept introduction:

A free radical chain reaction involves free radicals in a cyclic sequence of steps, called propagation steps, which are responsible for converting overall reactants into overall products. Throughout the sequence of propagation steps, also called the propagation cycle, there is no net consumption of free radicals. The overall reaction is obtained by summing just the propagation steps. An initiation step is responsible for producing the free radical that enters the propagation cycle. A termination step removes free radicals from the propagation cycle and is responsible for slowing the overall reaction. Radical addition to an alkene generally takes place so as to produce the more stable alkyl radical intermediate.