Question

Draw all constitutional isomers formed in each E2 reaction and predict the major product using the Zaitsev rule.

a.

b.

c.

d.

Short answer

The constitutional isomers are shown below, along with the major product.

Step-by-step solution

Definition of Zaitsev product

The product carrying more number of substitutions is considered to be a Zaitsev product.They are considered to be a major product due to the stability provided by the +I effect of the substituted alkyl groups.

Identification of the β hydrogens

Different products will be formed with the presence of more different types of $\text{β}$ hydrogens.

Representation of different types of beta Hydrogens

For a., two different types of $\text{β}$ hydrogens are present, hence two different products. The same goes with d. For c., three different types of $\text{β}$ hydrogens are present, therefore they give three products.

Since only one type of $\text{β}$ hydrogen is present, they give a single product.

Use of Zaitsev rule

The rule states that the more substituted product will be considered as the major product.

So, taking into account all the criteria, the constitutional isomers, along with their major products, are shown:

Representation of Zaitsev product in reaction a

Representation of Zaitsev product in reaction b

Representation of Zaitsev product in reaction c