Chapter 7.4, Problem 9CC

Interpretation Introduction

Interpretation:

Among the given set of reactions, the reaction that is expected to exhibit faster rate has to be predicted.

Concept Introduction:

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.

${\text{S}}_{\text{N}}2$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.

Leaving group: It is a fragment that leaves the chemical compound with pair of electrons in a heterolytic bond cleavage. The ${\text{S}}_{\text{N}}2$ reactivity increases in molecule with better leaving group.

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