Chapter 9.5, Problem 20P

(a)

Interpretation Introduction

Interpretation:

Among the given compounds, the one which is more reactive in a ${\text{S}}_{\text{N}}\text{1}$ reaction has to be identified.

Concept Introduction:

Vinyl and aryl halides: (${\text{S}}_{\text{N}}\text{1}$ reaction)

Vinylic halides and aryl halides do not undergo ${\text{S}}_{\text{N}}\text{1}$ reaction because vinyl and aryl cations are even more unstable than primary carbocation.

The positive charge on a vinylic or aryl cation would be an $sp$ carbon.  $sp$ carbons are more resistant to become positively charged than the $s{p}^2$ carbons.

(b)

Interpretation Introduction

Interpretation:

Among the given compounds, the one which is more reactive in a ${\text{S}}_{\text{N}}\text{1}$ reaction has to be identified.

Concept Introduction:

Vinyl and aryl halides: (${\text{S}}_{\text{N}}\text{1}$ reaction)

Vinylic halides and aryl halides do not undergo ${\text{S}}_{\text{N}}\text{1}$ reaction because vinyl and aryl cations are even more unstable than primary carbocation.

The positive charge on a vinylic or aryl cation would be an $sp$ carbon.  $sp$ carbons are more resistant to become positively charged than the $s{p}^2$ carbons.