I recently study organic chemistry and I read a book by Sana Jamshaid. I came across this compound and I cannot understand why it named **6-ethenyl-4-(prop-2'-enyl) octa-6-en-3-ol**:

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> [![6-ethenyl-4-(prop-2'-enyl) octa-6-en-3-ol](https://i.stack.imgur.com/GPA2Y.jpg)](https://i.stack.imgur.com/GPA2Y.jpg)
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I understand that the longest chain is 8, hence octa (but if we go up on the 4th longest can be 9) but I don't understand the **4-(prop-2’-enyl)**. Are there any explanations to why the compound named in such way? The double bond also sits on the 7th and not the 6th.