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Question 12.4: Cis-Trans Isomerism How many stereoisomers are possible for ...

Cis-Trans Isomerism

How many stereoisomers are possible for 2,4-heptadiene?

CH _{3}- CH = CH - CH = CH - CH _{2}- CH _{3} 2,4-Heptadiene

Strategy

To show cis-trans isomerism, each carbon of the double bond must have two different groups bonded to it.

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This molecule has two carbon–carbon double bonds, each of which shows cis-trans isomerism. As shown in the following table, 22 54 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
12.4

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