Chapter 7.9, Problem 32CC

Interpretation Introduction

Interpretation:

The starting material that represents a better choice for a rapid $\left({\text{S}}_{\text{N}}1\right)$ process has to be predicted and justified.

Concept Introduction:

Unimolecular nucleophilic substitution reaction$\left({\text{S}}_{\text{N}}1\right)$: Reaction of alkyl halide with nucleophile involves two step processes,

• Loss of leaving group, where the loss of leaving group from the substrate gives a carbocation intermediate.
• Nucleophilic attack: A nucleophile attacks the carbocation intermediate to afford the product.

Stability of carbocation: Generally $\left({\text{S}}_{\text{N}}1\right)$ process are observed for tertiary alkyl halides; the stability of carbocation as follows,

${\text{3}}^{\text{o}}\text{Carbocation}\text{>}\text{benzylic}\text{cation}\text{=}\text{allyl}\text{cation}\text{>}{\text{2}}^{\text{o}}\text{cation}\text{>}{\text{1}}^{\text{o}}\text{cation}\text{>}\text{methyl}\text{>}\text{vinylcation}$

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.

Resonance is an electron displacement effect for stabilizing a molecule through delocalization of bonding electrons in the pi orbital.

Delocalized electrons stabilize a compound. The extra stability gains from having delocalized electrons are called resonance stabilization or resonance energy.