Q9P-c - 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.${\text{CH}}_3{\text{CH}}_2{\text{CH =CHCH}}_3$

Step-by-Step Solution

Answer

Structure of the cis form of compound 

Structure of trans form of compound 

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 are on same side of the double bond. 

Step 2: Condition for cis and trans configuration

Condition for cis–trans isomerism in alkenes is that both of their carbons must be bonded to two different groups only then 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

Structure of given compound can exist in cis and trans form as both carbon has two different groups attached.

Cis-structure of given compound

Trans-structure of given compound