Tropylium cation

In organic chemistry, the tropylium ion is an aromatic species with a formula of [C₇H₇]. Its name derives from the molecule tropine (itself named for the molecule atropine). Salts of the tropylium cation can be stable, e.g., tropylium tetrafluoroborate. It can be made from cycloheptatriene (tropylidene) and bromine or phosphorus pentachloride.