Chapter 7.8, Problem 28CC

(a)

Interpretation Introduction

Interpretation: Identify the positions in the given substrate that will undergo ${\text{S}}_{\text{N}}2$ and ${\text{S}}_{\text{N}}\text{1}$ reaction.

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.

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.

Examples:

(b)

Interpretation Introduction

Concept Introduction:

${\text{S}}_{\text{N}}\text{1}$Reaction: it is a nucleophilic substitution reaction in which the rate determining step depends on one reactant. First step is the formation of more stable carbocation which is followed by the attack of nucleophile. Formation of more stable carbocation and the leaving group present in the substrate plays very important role in the reactivity of ${\text{S}}_{\text{N}}\text{1}$ reaction. The tertiary carbo cation substrate favors this mechanism strongly since it is the most stable species among the carbo cation.

Carbocation: it is carbon ion that bears a positive charge on it.

Carbocation stability order:

Carbo-cation Rearrangement: The carbo cation formed rearranges itself to given more stable carbo cation via methyl or hydrogen migration from the neighboring carbon present in the substrate.

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.