Q.29 - Organic Chemistry

Question

Which double bonds in the following natural products can exhibit stereoisomerism? Nerolidol is isolated from the angel’s trumpet plant, caryophyllene is present in hemp, and humulene comes from hops.

a.

b.

c.

Step-by-Step Solution

Answer

The double bonds that can exhibit stereoisomerism are marked in the following:-

Definition of Stereoisomers

The molecular formula and structure are the same but the orientation of the substituents across the double bond. They are designated as stereoisomers.

Cis and trans form

They can be of two types: 

• Cis/Z and 
• Trans/E. 

When both higher priority groups (higher atomic number groups) lie in the same direction, the configuration is named cis. The opposite position are named trans.

Representation of cis/Z and trans/E isomer

Observation of the structures

For Nerolidol, the double bond which is colored can exhibit stereoisomer because different groups are present at the double-bonded carbons. And for the rest, stereoisomer is not possible since similar groups are present at one side of the double-bonded carbon.

In the case of Caryophyllene, only that double-bonded carbon where different substituents are present exhibits stereoisomer. The double bond which exhibits stereoisomer is marked as shown.

All the double-bonded carbons in exhibit stereoisomers since different groups are present at the double-bonded carbons.