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While reading about cis/trans isomerism in cycloalkenes, I came across the following statement:

When the number of carbon atoms in a cycloalkane is less than 11, the cis form is more stable than the trans form. When it is greater than 11, the trans form is more stable than the cis form.

An obvious question came to my mind: What if the number of carbon atoms in the ring is "equal" to 11? Which form will be more stable - cis or trans? I think both will be of the same stability, but would like to have some clarification in this regard.

I searched my books and didn't find any specifications on the stability of cis or trans forms, for a ring containing exactly 11 carbon atoms. I read the answers to the question Stability of cis vs trans isomers? but they discuss only the cases "less than 11" and "greater than 11" but not "equal to 11".

orthocresol
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Vishnu
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    https://chemistry.stackexchange.com/questions/30940/relative-stability-of-cis-and-trans-cycloalkenes – Mithoron Jan 31 '20 at 16:20

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There is experimental data for the methoxy derivative: https://webbook.nist.gov/cgi/cbook.cgi?ID=C78289131&Units=SI&Mask=8

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I think that means the (Z) form is favored. I would think the situation is similar in the absence of the methoxy group.

Karsten
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  • Thank you for your answer. Will the relative energy difference between the cis/trans or E/Z forms be less for cycloundecene, compared to other cycloalkenes? – Vishnu Feb 01 '20 at 03:08
  • @Magnesium Here is a link to some more data: https://webbook.nist.gov/cgi/cbook.cgi?Source=1980TAS643-646&Units=SI&Mask=8 – Karsten Feb 01 '20 at 04:05