Question

Use curved arrows to show the movement of electrons in the following E2 mechanism. Draw the structure of the transition state.

Short answer

The mechanistic approach of the mentioned E2 elimination is shown below.

Step-by-step solution

Definition of E2 reaction

It is a one-step elimination process where the proton and the leaving group are in a syn-antiperiplanar position.

In this reaction, a single concerted step is followed where proton abstraction and removal of the leaving group take place simultaneously.

The rate of the reaction depends upon both the base and the reactant. Hence they are considered to be bimolecular elimination reactions.

Identification of the base

The base used here is ethoxide which is considered a strong base due to the localized electronic charge over the oxygen atom and electron-rich due to the +I effect of the ethyl group. Hence, they abstract protons followed by elimination.

Identification of the β hydrogens

The abstracted hydrogens are considered to be the $\text{β}$hydrogens as they are the first key part of elimination.

Representation of hydrogens

Formation of the more substituted product

That $\text{β}$hydrogen is considered where the major elimination product formed is found to be more substituted.

Hence, observing all the steps, the following mechanism is considered

Mechanistic approach for the formation of products

The side products obtained are ethyl alcohol and bromide ion.