Chapter 5, Problem 45P

Interpretation Introduction

Interpretation:

The classification of the formation of industrial preparation of methyl bromide from methanol by reaction with hydrogen bromide is to be done. The stepwise mechanism is to be written.

Concept introduction:

The reaction of methyl and primary alcohols with hydrogen halide mostly proceeds through ${\text{S}}_{\text{N}}2$ mechanism.

The reaction of tertiary alcohol with hydrogen halide proceeds through ${\text{S}}_{\text{N}}\text{1}$ mechanism.

The ${\text{S}}_{\text{N}}2$ reaction is the bimolecular nucleophilic substitution reaction whose rate determining step involved two reactants (both electrophile and nucleophile).

The ${\text{S}}_{\text{N}}\text{1}$ reaction is the unimolecular nucleophilic substitution reaction that means rate determining step involved only one reactant.

Formation of carbocation is the rate determining step in ${\text{S}}_{\text{N}}\text{1}$ mechanism.

The nucleophile (halide ion) attacks on the electrophilic carbon from opposite side of hydroxyl group (i.e. backside attack) in ${\text{S}}_{\text{N}}2$ mechanism.

The position of leaving group in reactant and that of nucleophile in the product are same in case of ${\text{S}}_{\text{N}}2$ mechanism and it may be same or different in case of ${\text{S}}_{\text{N}}\text{1}$ mechanism depending on the stability of carbocation.