of cyano substituents (7) is one of the most acidic compounds known with a computed pKa in DMSO of −30.4 (compared to for instance −20 for magic acid). Azulene is also a 10 π-electron system in which aromaticity is maintained by direct transannular bonding to form a fused 7–5 bicyclic molecule. References Annulenes Fully conjugated nonaromatic rings Ten-membered rings