Chapter 7, Problem 50PP

(a)

Interpretation Introduction

Interpretation:

The constitutional isomers of the given molecule ${\text{C}}_4{\text{H}}_{\text{9}}\text{Br}$ and their reactivity towards ${\text{S}}_{\text{N}}2$ reaction should be drawn and identified.

Concept introduction:

Isomers: compounds having same molecular formula but different structural arrangements.

• Constitutional isomers are isomers which have same molecular formula and different bond connectivity.

  

${\text{S}}_{\text{N}}2$Reaction: It is a nucleophilic substitution reaction in which the rate determining step depends on both of the molecules involved. The bond making and the bond breaking process happens simultaneously in this reaction.

Structure of the substrate plays a major role in ${\text{S}}_{\text{N}}2$ reaction. If the substrate consists of more substitution the rate of the reaction will becomes slower. Since the mechanism of ${\text{S}}_{\text{N}}2$ reaction proceeds through backside attack on the substrate it depends on steric factor that more groups attached near the leaving group the reactivity becomes slower.

Leaving group: it is a fragment that leaves the chemical compound with pair of electrons in a heterolytic bond cleavage.

(b).

Interpretation Introduction

Interpretation:

The constitutional isomers of the given molecule ${\text{C}}_4{\text{H}}_{\text{9}}\text{Br}$ and their reactivity towards $\text{E2}$ reaction should be drawn and identified.

Concept introduction:

• Elimination reaction: In elimination reaction, two substituents are removed from the substrate to give the product in presence of base. Elimination reactions are two types, $E1$ and $E2$.
• $E1$ reaction: elimination follows stepwise mechanism.
• $E2$ reaction: elimination follows concerted pathway of mechanism.
• Elimination of compound in presence of bulky base leads to less substituted alkene, in presence of strong base (not bulky) leads to more substituted alkene.