Wiktionary
isoindene
n. (context organic compound English) A flammable polycyclic hydrocarbon with the chemical formula C9H8, composed of a cyclohexadiene ring fused with a cyclopentadiene ring.
Wikipedia
Isoindene
Isoindene is a flammable polycyclic hydrocarbon with chemical formula CH. It is composed of a cyclohexadiene ring fused with a cyclopentadiene ring.