Chapter 8, Problem 8.48P

Interpretation Introduction

Interpretation:

It is to be explained if it is possible to tell whether the given reaction takes place via an $\text{E1}$ or an $\text{E2}$ reaction.

Concept introduction:

The $\text{E1}$ reaction proceeds with the formation of carbocation intermediate by the elimination of the leaving group in first step. In the second step, the hydrogen atom adjacent to the carbocation is removed by the base to form a double bond. As the carbocation is planar, the elimination product would be a mixture of diastereomers when the double bonded carbon atoms are asymmetrically substituted.

In case of $\text{E2}$ elimination, the eliminating groups (leaving group and $\text{H}$) must be anti to each other. If the substrate has two hydrogen atoms attached to the carbon adjacent to leaving group, then elimination can occur two ways with each hydrogen atom. In one case, one hydrogen atom is eliminated along with the leaving group, and in another case, the other hydrogen atom is eliminated along with leaving group, thus forming a mixture of diastereomers.