Question

Draw the product formed by the reaction of potassium t-butoxide with (1S,2S)-1-bromo-2-methyl-1-phenylbutane (shown below). (Draw the correct stereoisomer of the product.)

Draw the product formed by the reaction of potassium t-butoxide with (1S,2S)-1-bromo-2-methyl-1-phenylbutane (shown below). (Draw the correct stereoisomer of the product.)

Answer 1

Concepts and reason

A reaction is given whose product needs to be drawn. Firstly, identify whether the product formed through substitution reaction or the elimination reaction then, write the product formed.

Thus, identify the nucleophile and the leaving group in the given reaction and accordingly form the product of the reaction.

Fundamentals

Elimination reaction can be categorized as, ${\rm{E}}1$ and ${\rm{E}}2$ depending on the type of mechanism followed.

• ${\rm{E}}1$ reaction is unimolecular elimination reaction which takes place between a haloalkane and a nucleophile. The reaction takes place in two step through a carbocation intermediate. In haloalkane, the order of reactivity for the ${\rm{E}}1$ reaction is, $3^\circ > 2^\circ > 1^\circ > {\rm{C}}{{\rm{H}}_3}$ like the stability of carbocation.

• ${\rm{E}}2$ reaction is bimolecular elimination reaction which takes place between a haloalkane and a nucleophile. The reaction takes place in one step through a transition state. Consider the following scheme of a ${\rm{E2}}$ reaction:

In haloalkane, the order of reactivity for the ${\rm{E}}2$ substitution reaction is, $3^\circ < 2^\circ < 1^\circ < {\rm{C}}{{\rm{H}}_3}$ .

Substitution reaction can be categorized as, ${{\rm{S}}_{\rm{N}}}1$ and ${{\rm{S}}_{\rm{N}}}2$ depending on the type of mechanism followed.

• ${{\rm{S}}_{\rm{N}}}1$ reaction is unimolecular nucleophilic substitution reaction which takes place between a haloalkane and a nucleophile. The reaction takes place in two step through a carbocation intermediate.

In haloalkane, the order of reactivity for the ${{\rm{S}}_{\rm{N}}}1$ substitution reaction is, $3^\circ > 2^\circ > 1^\circ > {\rm{C}}{{\rm{H}}_3}$ like the stability of carbocation.

• ${{\rm{S}}_{\rm{N}}}2$ reaction is bimolecular nucleophilic substitution reaction which takes place between a haloalkane and a nucleophile. The reaction takes place in one step through a transition state.

In haloalkane, the order of reactivity for the ${{\rm{S}}_{\rm{N}}}2$ substitution reaction is, $3^\circ < 2^\circ < 1^\circ < {\rm{C}}{{\rm{H}}_3}$ .

Identify the structure of haloalkane and strength of nucleophile in the given compound as shown below:

As secondary haloalkane is present in the presence of strong nucleophile, that is, tertiary butoxide in polar aprotic solvent. So, the reaction will proceed through Elimination $\left( {{\rm{E2}}} \right)$ mechanism.

Write the product of the given reaction following the E2 mechanism with the correct stereochemistry of the product as shown below:

E2 elimination takes place in one step, therefore, dehydrohalogenation take place and result in the formation of alkene as shown above.

Ans: