I want to know which is the correct parent chain in this compound: enter image description here

Is it the one inside the loop, or the longer one that includes the part to the left of the allyl group?

I know that once a functional group of highest priority has been selected, lower-priority functional groups take on the same priority as substituents. How does this rule work with two instances of the same functional group? Do we select the parent chain including both, or select one of them and the longest chain possible thereafter?


1 Answer 1


According to the IUPAC 1993 Blue Book the name of the compound would be : 3-Pentylsept-1,6-diene (The circled one being the parent chain)

According to the new IUPAC 2013 Blue Book the name of the compound would be : 5-(1-ethylidene)-dec-1-ene (The longest continuous chain being the parent chain)

The reason being the new Rule in the 2013 conventions that state that the longest chain irrespective of the degree of unsaturation will be the parent chain.

  • $\begingroup$ The substituent at C-5 is a vinyl group, not ethylidene. Ethylidene would have the double bond in the trisubstituted position and have an E/Z designation. 5-Vinylundec-1-ene. $\endgroup$
    – user55119
    Sep 8, 2021 at 19:53
  • $\begingroup$ Both suggested names are wrong. It's "hepta" not "sept", and it's "ethenyl" not "(1-ethylidene)". $\endgroup$
    – Loong
    Jan 6, 2022 at 11:44

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