Polycyclic compound

They come in sizes of three atoms and upward, and in combinations of linkages that include tethering (such as in biaryls), fusing (edge-to-edge, such as in anthracene and steroids), links via a single atom (such as in spiro compounds), bridged compounds, and longifolene.

Though poly- literally means "many", there is some latitude in determining how many rings are required to be considered polycyclic; many smaller rings are described by specific prefixes (e.g., bicyclic, tricyclic, tetracyclic, etc.

), and so while it can refer to these, the title term is used with most specificity when these alternative names and prefixes are unavailable.

An example of a polycyclic compound based on a nitrogen cage is hexanitrohexaazaisowurtzitane.

There is a scheme for naming polycyclic compounds using square brackets [] and numbers.

Longifolene , a terpene natural product , and an example of a tricyclic molecule
Cholesterol , another terpene natural product, in particular, a steroid , a class of tetracyclic molecules
Benzo[ a ]pyrene , a pentacyclic compound both natural and man-made
Pagodane , a man-made polycyclic compound
Brevetoxin A , a natural product with ten rings, all fused, and all heterocyclic , and a toxic component associated with the organisms responsible for red tides . The R group at right refers to one of several possible four-carbon side chains. (See Brevetoxin .)