Q.17 - Organic Chemistry

Question

Given that an E2 reaction proceeds with anti periplanar stereochemistry, draw the products of each elimination. The alkyl halides in (a) and (b) are diastereomers of each other. How are the products of these two reactions related? Recall from Section 3.2A that ${\mathbf{\text{-C}}}_{\mathbf{6}}{\mathbf{\text{H}}}_{\mathbf{5}}$ is a phenyl group, a benzene ring bonded to another group.

a.

b.

Step-by-Step Solution

Answer

The products formed from the given reactions are:

The products a. and b. are stereoisomers with each other.

Definition of Diastereomers

Isomers have the same molecular formula, structure, and bonding pattern, but no mirror image relationships are known as diastereomers.

 

The reactants of both the reactions are diastereomers with each other since there is a change in the orientation of the groups at one carbon.

Antiperiplanar orientations

To undergo elimination reactions, the protons and the leaving group must be in a trans-position with each other to give an elimination product.

Representation of anti-periplanar orientation

Relation between the products

The products formed are stereoisomers with others since, in the case of the first structure, the high priority phenyl rings lie in the opposite direction(trans alkene). In contrast, for the second structure, they are at the same position(cis alkene).

Representation of the diastereomers

Hence, the products formed from the given reactions are:

Formation of product from a

The above reaction gives a trans product.

Formation of product from b

The above reaction gives a cis product. The products a. and b. are stereoisomers with each other.