| cis- (top) and trans-Cyclooctene[1] | |
|---|---|
|
(E)-Cyclooctene |
|
|
Other names
cis-Cyclooctene |
|
| Identifiers | |
| CAS number | 931-87-3 |
| PubChem | 638079 |
| ChemSpider | 553642 |
| Jmol-3D images | Image 1 |
|
|
|
|
| Properties | |
| Molecular formula | C8H14 |
| Molar mass | 110.2 g mol−1 |
| Density | 0.846 g/mL |
| Melting point |
-16 °C, 257 K, 3 °F |
| Boiling point |
145-146 °C |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) | |
| Infobox references | |
Cyclooctene is a cycloalkene with an eight-membered ring. It is notable because it is the smallest cycloalkene that can exist as either the cis- or trans-isomer with the cis-isomer more common. Its most stable cis stereoisomer can adopt various conformations, the most stable one being shaped like a ribbon[2] ; its most stable trans-conformer is shaped like the 8-carbon equivalent chair conformation of cyclohexane.
| cis-Cyclooctene | trans-Cyclooctene |
trans-Cyclooctene is the smallest cycloalkene in which the trans-isomer is stable at room temperature (compared to cyclopropene for cis). This is because trans-cycloalkenes have a longer bridging distance between the two allylic carbons than their respective cis-cycloalkenes. As a result, eight carbons is the minimum ring size required to form a trans-cycloalkene without incurring severe angle strain which is the cause for the instability of smaller trans-rings. trans-Cycloheptene and trans-cyclohexene can exist, but they are very unstable at room temperature. trans-Cyclooctene exists in a helical conformation with the carbon chain lying above the double bond on one side and below it on the other, leading to chirality (as depicted to the right).
trans-Cyclooctene was first synthesized on a preparatory scale by Arthur C. Cope beginning from N,N,N-trimethylcyclooctylammonium iodide and using a Hofmann elimination.[3] Other methods exist where the trans-isomer is synthesized from the cis-isomer in several synthetic steps. In addition, a photochemical method exists for this conversion in just one step:
Although the cis-trans equilibrium is unfavorable, the reaction can be driven to completion by trapping of the trans-isomer by complexation with silver.[4]
|
||||||||