Cyclooctene is the smallest cycloalkene that can be isolated as both the cis- and trans-isomer.

[2] cis-Cyclooctene is shaped like the 8-carbon equivalent chair conformation of cyclohexane.

Cyclooctene undergoes ring-opening metathesis polymerization to give polyoctenamers, which are marketed under the name Vestenamer.

[3] cis-Cyclooctene (COE) is a substrate known for quite selectively forming the epoxide, as compared to other cycloalkenes, e.g. cyclohexene.

Therefore, if radicals are around, they tend to form epoxide via an addition-elimination mechanism.