Chapter 10.9, Problem 24P

(a)

Interpretation Introduction

Interpretation:

Among the following compounds the compound which reacts faster in ${\text{S}}_{\text{N}}\text{2}$ reaction has to be identified.

Concept Introduction:

Substitution reaction is a reaction in which an atom or group of a molecule is replaced by another atom or group.

S_N2 reaction refers to bimolecular substitution reaction in which rate of the reaction depends on concentration of two reactive species.

(b)

Interpretation Introduction

Interpretation:

Among the following compounds the compound which reacts faster in ${\text{E}}_{\text{1}}$ reaction has to be identified.

Concept Introduction:

For an E1/E2 reaction, when same alkyl group is present with the leaving group, the relative reactivity of alkyl halide is,

$RI>RBr>RCl>RF$

(c)

Interpretation Introduction

Interpretation:

Among the following which reacts faster in S_N1 reaction is to be identified.

Concept Introduction:

Substitution reaction is a reaction in which an atom or group of a molecule is replaced by another atom or group.

S_N1 reaction refers to unimolecular substitution reaction in which rate of the reaction depends on concentration of only one reactive species.

(d)

Interpretation Introduction

Interpretation:

Among the following which reacts faster in E2 reaction is to be identified.

Concept Introduction:

• Elimination reaction is a reaction in which an atom or group of a molecule is eliminated and a double bond is formed.
• This type of reaction primarily occur in alkyl/aryl halides.
• Elimination reactions are of two types – E1 elimination and E2 elimination.
•  E2 elimination is a concerted reaction and involves formation of transition state in which both proton and halide are removed in one single step.
• E2 elimination follows Zaistev’s rule that the major product is usually the most substituted alkene.  Thus E2 reaction is regioselective if the leaving group is too weak then least substituted alkene is formed.
• Primary and secondary halides undergo E2 elimination whereas tertiary halides undergo E1 elimination as tertiary carbocation formed is more stable.
• Allylic and benzylic halides undergo both E1 and E2 reactions.
• Presence of high concentration of strong base favors E2 reaction.