Chapter 20, Problem 20.22P

(a)

Interpretation Introduction

Interpretation: The thermodynamic and kinetic products that are expected to be formed on addition of one mole of ${\text{Br}}_{\text{2}}$ to the given diene have to be found.

Concept Introduction:

Kinetic and Thermodynamic products:

• • If the reactants gives a product via small $\text{activation}\text{energy}\left({\text{E}}_{\text{a}}\right)$, then the resulted product will be readily formed from the reactants and it is known as  Kinetically controlled product.
• • If the reactants gives a product via large $\text{activation}\text{energy}\left({\text{E}}_{\text{a}}\right)$, then the resulted product will be least energetic than the reactants and it is known as Thermodynamically controlled product.

 Example:

The reaction of $\text{HBr}$ and $\text{1,3-butadiene}$ takes place as shown in the following mechanism. The mechanism shows the intermediates and the corresponding products.

Product A is formed from more stable intermediate. So, it would have been formed with less expense of energy and it would have been formed readily. Therefore, product $A$ is the kinetically controlled product.

Product B is formed from less stable intermediate. So, it would have been formed with more expense of energy. Hence, product B would have not been formed readily and it will be with more energy than that of the reactant. Therefore, product $B$ is the thermodynamically controlled product.

(b)

Interpretation Introduction

Interpretation: The thermodynamic and kinetic products that are expected to be formed on addition of one mole of ${\text{Br}}_{\text{2}}$ to the given diene have to be found.

Concept Introduction:

Kinetic and Thermodynamic products:

• • If the reactants gives a product via small $\text{activation}\text{energy}\left({\text{E}}_{\text{a}}\right)$, then the resulted product will be readily formed from the reactants and it is known as  Kinetically controlled product.
• • If the reactants gives a product via large $\text{activation}\text{energy}\left({\text{E}}_{\text{a}}\right)$, then the resulted product will be least energetic than the reactants and it is known as Thermodynamically controlled product.

 Example:

The reaction of $\text{HBr}$ and $\text{1,3-butadiene}$ takes place as shown in the following mechanism. The mechanism shows the intermediates and the corresponding products.

Product A is formed from more stable intermediate. So, it would have been formed with less expense of energy and it would have been formed readily. Therefore, product $A$ is the kinetically controlled product and it has been formed from 1,2-addition.

Product B is formed from less stable intermediate. So, it would have been formed with more expense of energy. Hence, product B would have not been formed readily and it will be with more energy than that of the reactant. Therefore, product $B$ is the thermodynamically controlled product and it has been formed from 1,4-addition.