Question

Draw the major E2 reaction product formed when cis-1-chloro-2-ethylcyclohexane (shown below) reacts with hydroxide ion in DMSO.

Answer 1

Concepts and reason

A reaction is given whose elimination product needs to be drawn which must follow the ${\rm{E2}}$ elimination mechanism. ${\rm{E2}}$ elimination takes place in one step in which nucleophile attacks the carbon containing a leaving group and leads to the formation of product.

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, $3^\circ < 2^\circ < 1^\circ < {\rm{C}}{{\rm{H}}_3}$ .

Identify the haloalkane, nucleophile, and ${\rm{\beta }} - {\rm{carbon}}$ from which the loss of H take place in the given compound as shown below:

Write the product of the given reaction according to Zaitsev’s rule following the E2 mechanism as shown below:

Ans: