Q9P-b - Organic Chemistry (Mcmurry)

Question

Which of the following compounds can exist as pairs of cis-trans isomers? Draw each cis-trans pair, and indicate the geometry of each isomer.${\left({\text{CH}}_3\right)}_2{\text{C =CHCH}}_3$

Step-by-Step Solution

Answer

Structure of cis form of compound is: Not possible

Structure of trans form of compound is: Not possible

Step-by-Step Solution Step 1: Cis and Trans configuration

Cis configuration is when two groups are on the same face of the double bond, and trans configuration is when the groups are on opposite faces. 

Both isomers are stable, and neither can be converted into the other without breaking and reforming chemical bonds. 

Cis alkenes are less stable than their trans form as there is steric strain between the two bulky substituents on the same side of the double bond. 

Step 2: Condition for cis and trans configuration

The condition for cis-trans isomerism in alkenes is that their carbons must be bonded to two different groups. Only then is cis-trans isomerism possible.

If one of their carbons bonded to two identical groups, then cis-trans isomers can’t exist

Step 3: Structure of given compound in cis and trans form

The structure of a given compound cannot exist in a cis, and trans form as one of the carbon has identical groups attached. Here, only one structure is possible that is:

Structure of given compound