Answer:
a. (2Z,4Z)-hexa-2,4-diene
b. (2E,4E)-hexa-2,4-diene
c. (Z)-hexa-1,4-diene
d. hexa-1,5-diene
Explanation:
IUPAC naming rules for E/Z stereoisomerism
Why we call it as E or Z
If both priority groups are on the same side we can say that they have Z configuration. And when both priority groups are on the opposite side we can say that they have E configuration.
How to select priority groups
We select the priority groups by their atomic number. We give higher priority to that group which has higher atomic number.
a. (2Z,4Z)-hexa-2,4-diene
As we can see in the attached structure that both priority groups attached to both double bonds are in the same side or we can say that they are cis to each other. When both priority groups are on same side or cis to each other we call it as Z.
b. (2E,4E)-hexa-2,4-diene
As we can see in the attached structure that both priority groups attached to both double bonds are on opposite side or we can say that they are trans to each other. When both priority groups are on opposite side or trans to each other we call it as E.
c. (Z)-hexa-1,4-diene
As we can see in the attached structure that the double bond located on terminal of the chain have two same groups (hydrogen) on one side so this double bond have no any stereo isomer having E/Z configuration.
As we can see in the 2nd double bond that both priority groups are in the same side or we can say that they are cis to each other. When both priority groups are on same side or cis to each other we call it as Z.
d. hexa-1,5-diene
As we can see in the attached structure that both double bonds of the chain have two same groups (hydrogen) on one carbon so these double bonds have no any stereoisomers having E/Z configuration.
