Question 12.4: How many stereoisomers are possible for 2,4-heptadiene? CH3-...

Strategy
To show cis-trans isomerism, each carbon of the double bond must have two different groups bonded to it.
Solution
This molecule has two carbon–carbon double bonds, each of which shows cis-trans isomerism. As shown in the following table, 2^2 =4 stereoisomers are possible. Line-angle formulas for two of these dienes are drawn here.

Double-Bond
C_2–C_3              C_4–C_5
(1) trans          trans
(2) trans             cis
(3) cis               trans
(4) cis                  cis

Problem 12.4
Draw structural formulas for the other two stereoisomers of 2,4-heptadiene.