Geometric Isomers with multiple double bonds

[Kimberly Wagas 1H]

In page 17 of the Intro to Organic Chemistry textbook, there are two examples of geometric isomers with multiple double bonds? Which double bond do you consider when deciding if an isomer is cis or trans?

[Jiangyuan Luo 1K]

We consider the C=C between the third and the fourth carbon atoms. When we are talking about geometric isomers due to C=C, for each of the carbon atom on both sides of the double bonds, it has to be connected by two different chain. For example, the first carbon atom is connected to two hydrogen atoms and so does the eighth carbon atom. Thus there is no geometric isomer about them.