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From the rules that I know, I will name the above compound as 3-propyl-penta-1,3-diene because maximum number of functional groups (double bonds in this case) are in the five numbered carbon chain.

However chemdraw names the above compound as 3-ethylidene-hex-1-ene. Why? Am I missing some rule?

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    $\begingroup$ This compound also has stereochemistry ($E/Z$). $\endgroup$ – Mathew Mahindaratne Feb 22 at 16:29
  • $\begingroup$ If we ignore E/Z nomenclature at the moment @Mathew Mahindaratne , what about the main name? $\endgroup$ – Light Yagami Feb 22 at 16:31
  • $\begingroup$ Naming rules include identifying the longest carbon chain. $\endgroup$ – z1273 Feb 22 at 16:49
  • $\begingroup$ I know that, but there is another rule that if there are functional groups present, we choose the longest chain which has maximum number of functional groups, and since it contains two double bonds IMO 5 numbered chain should be considered as parent chain. Can I get a reference? @z1273 $\endgroup$ – Light Yagami Feb 22 at 16:58
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