[robstamos]

Simple question: Which is more stable: E cyclooctene or Z cyclooctene?

My professor marked the correct answer as E cyclooctene on the exam, but I am almost certain this is a mistake. Can anyone verify this for me before I email him?

[OrganicH2O]

Z is more stable due to relatively small ring size making trans unstable.

[AWK]

E (trans) isomers of cycloalkenes become more stable than Z (cis) isomers once the ring contains twelve or more carbon atoms. Z-cyclooctene exists. The energy difference between cis- and trans-cyclooctene is approximately 38.5 kJmol^-1.

[mjc123]

Is "CIA" autocorrect for "cis"?

[clarkstill]

The energy difference between cis- and trans-cyclooctene is approximately 38.5 kJmol^-1.

Do you have a source for this? According to NIST (and references therein) the difference in standard heat of formation is about 3 kcal/mol (~12 kJ/mol).

https://webbook.nist.gov/cgi/cbook.cgi?ID=C931895&Mask=1E9F
https://webbook.nist.gov/cgi/cbook.cgi?ID=C931873&Units=SI&Mask=1F

But I agree that clearly (Z) is lower in energy.