Question

What is the major E2 elimination product formed from each alkyl halide?

a.

b.

Short answer

The major E2 product formed is given below:

Step-by-step solution

Anti-periplanar orientation

The $\text{β}$hydrogen and the leaving group must be in an antiperiplanar position to give an elimination product. If the antiperiplanar position is not present, then the bond must be rotated to obtain the same.

Stability of the alkene

Cis alkenes suffer from steric repulsion since both the higher priority groups lie in the same orientation. In the case of trans alkenes, steric repulsion is not there due to the higher priority groups lying in the opposite direction.

This is why cis alkenes are less stable than their trans counterpart. Hence trans-alkene is considered to be a major product.

Representation of steric repulsion

E2 elimination products

The major E2 elimination product formed is given below:-

a.

Representation of E2 reaction scheme of a

b.

Representation of E2 reaction scheme of b