Cyclooctatetraene

• COT
• Cyclo -1 ,3,5,7 - tetraene
• Annulene

Yellow liquid with an unpleasant odor

Liquid

0.93 g · cm -3

0 ° C

142-143 ° C

10.5 hPa ( 20 ° C)

Insoluble in water

1.5381 (20 ° C)

Risk

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Cyclooctatetraene (COT ) is an organic chemical compound selected from the group of cyclic hydrocarbons. The compound with the formula C8H8 has four conjugated C = C double bonds.

In contrast to benzene ( C6H6) COT is not among the aromatic hydrocarbons, as it is based on the number of its π - electrons does not correspond to the Hückel rule and is non-planar, but has tub shape. Thus cyclooctatetraene neither an aromatic nor a Antiaromat. Due to the lack of aromatic stabilization, it is rather ordinary polyenes comparable, however, due to the ring strain caused by the bond angle deformation of increased reactivity.

The tub-shaped COT molecule can be used as chelate - form metal complexes - similar to 1,5-cyclooctadiene ( COD). By the addition of two electrons, for example by transfer from a metal, from the COT eight π -electron planar aromatic anion C8H82 - cyclooctatetraenyl. This aromatic corresponds with ten electrons of the Hückel rule. A well-known example of a complex with planar cyclooctatetraenyl ligands is the uranocene.

Representation

COT was first synthesized in 1905 by Richard Willstätter from pseudopelletierine.

COT can be produced by cyclotetramerization Reppe from ethyne:

Another synthesis starts from the Cuban. In the presence of rhodium catalysts, the syn tricyclooctadiene is first formed which can then be converted to the cyclooctatetraene at 50-60 ° C thermally.