Chapter 7, Problem 80IP

(a)

Interpretation Introduction

Interpretation:

The passible mechanism should be drawn under given reaction conditions.

Concept Introduction:

${\text{S}}_{\text{N}}2$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 major role in the reactivity of ${\text{S}}_{\text{N}}2$ reaction. If the substrate is more substituted then 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 if more groups attached near the leaving group the reactivity becomes slower. The ${\text{S}}_{\text{N}}2$ reactivity increases in molecule with better leaving group. The reactivity increases in the order as follows,

  

Leaving group: it is a fragment that leaves substrate with a pair of electrons via heterolytic bond cleavage.

Nucleophile: donates pair of electrons to positively charged substrate resulting in the formation of chemical bond.

(b)

Interpretation Introduction

Interpretation:

The reactivity of the reaction under given conditions should be identified.

Concept Introduction:

Rate of reaction is depends upon the concentration of substrate and concentration of base. Because in a bimolecular reaction, there should involves two chemical entities.

Equation for the rate of E2 reaction is,

    $\text{Rate}\text{=}\text{k}\text{[}\text{substrate}\text{]}\text{[}\text{base}\text{]}$

Rate Equation: It describes the rate of the reaction with respect to the concentration of the reactants participated in the reaction.

The relationship between the rate of the reaction and concentrations of the given nucleophile and alkyl halide can be represented as follows.

  $\text{Rate}\text{α }\left[\text{alkyl halide}\right]\left[\text{nucleophile}\right]$

Thus,

  $\text{rate}\text{=}\text{k[alkyl}\text{halide][nucleophile]}$ ,

 Where, k is the rate constant.