Trans-Cyclooctene


trans-Cyclooctene is an organic compound with the formula 62. It is a colorless liquid. Cyclooctene is notable as the smallest cycloalkene that is readily isolated as its trans-isomer. The cis-isomer is much more stable.
cis-Cyclooctene trans-Cyclooctene

The molecule is shaped like the 8-carbon equivalent chair conformation of cyclohexane. It is chiral. This type of chirality is defined as planar chirality. It has been resolved into optical isomers.

Preparation

trans-Cyclooctene was first synthesized on a preparatory scale by Arthur C. Cope with a Hofmann elimination reaction of N,N,N-trimethylcyclooctylammonium iodide. The reaction gives a mixture of cis and trans isomers, and the trans isomer is selectively trapped as a complex with silver nitrate. Other methods exist where the trans-isomer is synthesized from the cis-isomer in several synthetic steps. In addition, a photochemical method exists for the direct cis–trans isomerisation.
Although this equilibrium strongly favours the more stable cis form, the reaction can be driven towards the trans by trapping with silver ions.