The structure of a tropane ring is chemically known as a piperidine fused to a cyclohexane, forming a bicyclic structure. More specifically, it's referred to as a tetrahydropyridine fused to a cyclohexane, giving the tropane ring its characteristic 7-membered and 6-membered ring system.

Some chemicals with similar structures include:

• Tropine (a related compound)
• Atropine
• Scopolamine
• Hyoscyamine

These are all alkaloids found in plants of the nightshade family, such as datura, belladonna, and mandrake.

Other similar structures include:

• Piperidine (a 6-membered ring)
• Tetrahydrofuran or tetrahydropyran (cyclic ethers with a similar fusion concept)

These are all related in terms of their bicyclic or fused-ring systems, and they share structural similarities with the tropane ring.