Cyclooctene is notable because it is the smallest cycloalkene that can exist stably as either the cis or transstereoisomer, with cis-cyclooctene being the most common. Theoretical analysis implies a total of 16 conformational and configurational isomers, all chiral, forming 8 enantiomeric pairs.[1] The cis isomer can adopt various conformations, the most stable one being shaped like a ribbon.[1] The most stable conformation of trans-cyclooctene is shaped like the 8-carbon equivalent of the chair conformation of cyclohexane.
Longer cycloalkene rings such as the ten-carbon cyclodecene also occur as cis and trans isomers.
References
^ abNeuenschwander, Ulrich; Hermans, Ive (2011). "The conformations of cyclooctene: Consequences for epoxidation chemistry". J. Org. Chem.76 (24): 10236–10240. doi:10.1021/jo202176j. PMID22077196.