I know that one of the more stable structures of [10]annulene or cyclodecapentaene is planar boat-shaped. But that means the hybridization state of the carbons must have changed to suit the geometry. What does it change to? And how are the hybridized orbitals distributed such that the double bonds remain intact?

Edit: I have encountered this molecule only once and am not familiar with the naming convention. For much the same reason, I don't know the exact structure of the most stable isomer of the compound. So even though I was more interested in the boat-shaped isomer of the compound, I think to do away with the ambiguity of the question, I should mainly ask for the most stable isomer of the molecule, viz., trans,cis,cis,cis,cis-isomer.

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    $\begingroup$ A mess. The molecule wants to be aromatic according to its pi electron conjugation but sterically it can't get there. Bring on the methylene bridge! $\endgroup$ May 6, 2019 at 14:35
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    $\begingroup$ Which isomer and which atom? Also by the time you know about such molecules, you should know that molecules distort as they need, not as "imaginary" hybridisation tells you. $\endgroup$
    – Mithoron
    May 7, 2019 at 18:02
  • $\begingroup$ @Mithoron That's true (but I'm not at that level). I saw this molecule on a test that required me to comment if it had any atom which had a hybridization other than sp2. And surprisingly, the answer said that it did. The question is meant for its most stable isomer. And for any atom which might not be sp2 hybridized. $\endgroup$
    – Blue
    May 7, 2019 at 18:15
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    $\begingroup$ I could do pretty much the same analysis as I did for your previous question. However, because there are ten carbons here it will take more time... $\endgroup$ May 7, 2019 at 22:14
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    $\begingroup$ You do need to clarify the question, though. It is something that Mithoron has already pointed out: cyclodecapentaene has various possible isomers; the most stable (according to Wikipedia) is the trans,cis,cis,cis,cis-isomer, so presumably this is what you are interested in, but the picture you have chosen is the cis,cis,cis,cis,cis-isomer. The Wikipedia article has quite a nice summary of the isomers. $\endgroup$ May 8, 2019 at 1:37

1 Answer 1


enter image description here

This here is the trans,cis,cis,cis,cis-isomer of [10]annulene or cyclodecapentaene, according to a few textbooks and some websites, this here is the most stable isomer of [10]annulene.

As you can see,this is not planar and contains only one trans structure.Here I don't see any carbon with hybridization other than sp2.


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