In the field of
organic chemistry, a
polycyclic compound is an
organic chemical featuring several closed rings of atoms, primarily carbon. These ring substructures include
cycloalkanes,
aromatics-, and other ring types. 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), and
bridged cyclics such as the
longifolene example. 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.