Valence Isomer - Cyclooctatetraene

Cyclooctatetraene

The valence isomers are not restricted to isomers of benzene. Valence isomers are also seen in the series (CH)₈. Due to the larger number of units, the number of possible valence isomers is also greater and at least 21:

• Valence isomers of cyclooctatetraene

• Cyclooctatetraene (COT)

• Barrelene

• Cubane

• Cuneane

• Semibullvalene

• 1,5-dihydropentalene

• Bicycloocta-2,5,7-triene

• 2a,2b,4a,4b-Tetrahydrocyclopropapentalene

• Bicycloocta-2,4,7-triene. Tautomer with COT by thermal 6e process or photochemical 4e process

• Tricycloocta-3,8-diene. Isomerises to semibullvalene at room temperature, stable at −60 °C

• Tricycloocta-3,7-diene. The dimer of cyclobutadiene occurs as a cis isomer and a trans isomer. Both isomers convert to COT (symmetry forbidden hence stable) with a half-life of 20 minutes at 140 °C

• Tetracyclo octa-7-ene is only known as its 4-carbomethoxy derivative.

• Tetracyclo octa-7-ene has been prepared from benzvalene and isomerises to COT

• Pentacyclooctane (octabisvalene) is the third saturated valence isomer. The (Z)-3,7-phenylsulfonyl derivative is stable up to 200 °C.

• Tricycloocta-3,5-diene (octavalene) was reported synthesised from homobenzvalene and converts to COT at 50 °C