Question

What is the major stereoisomer formed when each alkyl halide is treated with ${\mathbf{\text{KOC(CH}}}_{\mathbf{\text{3}}}{\mathbf{\text{)}}}_{\mathbf{\text{3}}}$?

a.

b.

Short answer

The mechanical 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.

Since the rate of the reaction depends upon both the base and the reactant, so, they are considered to be bimolecular elimination reactions.

Identification of the base

The base used here is bulky tert-butoxide. It is considered to be a strong base due to the localized electronic charge over the oxygen atom. It is also electron-rich due to the +I effect of the tert-butyl group.

Hence, they abstract protons readily and undergo elimination at a fast rate.

Identification of the β  hydrogens

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

Representation of the beta hydrogens

Therefore, the mechanistic approach of the mentioned E2 elimination is shown below:

Representation of the mechanism schemes from a

Representation of the mechanism schemes from b