Compounds based on a seven-membered ring fused to a five-membered ring. Heat can rearrange them to NAPHTHALENES which have two fused six-membered rings. They are similar to guaiazulenes which are SESQUITERPENES with a six-membered ring fused to a five-membered ring.

Synonyms: Bicyclo(5.3.0)Decapentaenes, 0, Cyclopentacycloheptenes, Azulenes