Q11.59CP - Chemistry: Molecular Nature Of Matter And Change

Question

Linoleic acid is an essential fatty acid found in many vegetable oils, such as soy, peanut, and cottonseed. A key structural feature of the molecule is the cis orientation around its two double bonds, where R1 and R2 represent two different groups that form the rest of the molecule.

1. How many different compounds are possible, changing only the cis-trans arrangements around these two double bonds?
2. How many are possible for a similar compound with three double bonds?

Step-by-Step Solution

Answer

For geometrical isomerism, the molecule must have restricted rotation and have two different groups or molecules around a carbon-carbon double bond.

The answer for

a) four

b) four

Step 1: Definition

The stereoisomerism in which a molecule is having same molecular formula and structure but a different arrangement of atoms or molecules is known as geometrical isomerism. Cis and trans are two types of geometrical isomers.

 

In a cis isomer, molecules are on one side of the double bond.

In a trans isomer, molecules are on the other side of the double bond.

 

Step 2: Total no. of compounds with two double bonds

The total number of compounds with two double bonds is four by changing the position of  ${\mathbf{R}}_{\mathbf{1}}$  and  ${\mathbf{R}}_{\mathbf{2}}$.

Step 3: Total no. of compounds with three double bonds

From the above, it is clear that the total number of compounds with three double bonds is four by changing the position of  ${\mathbf{R}}_{\mathbf{3}}$ and  ${\mathbf{R}}_{\mathbf{4}}$.