monocyclic

Monocyclic is an adjective used to describe a molecule or system that contains a single ring. It is a common term in chemistry and related fields for distinguishing structures with one ring from those with two or more rings.

In chemistry, a monocyclic compound has one ring in its core skeleton. This ring can be aromatic or aliphatic. Monocyclic rings can be saturated, unsaturated, or heterocyclic (containing atoms other than carbon such as nitrogen or oxygen). Examples of monocyclic aromatic compounds include benzene, toluene, and phenol, while examples of monocyclic alicyclic compounds include cyclohexane and cyclopentane. Heterocyclic monocyclic compounds include pyridine, thiophene, and imidazole, where heteroatoms replace one or more ring carbons.

The term is often contrasted with bicyclic and polycyclic, which describe molecules with two or more rings that are fused or linked. Monocyclic compounds may be part of larger synthetic schemes or serve as building blocks for more complex structures in pharmaceuticals, agrochemicals, and materials science. In nomenclature, monocyclic indicates that a single ring forms the main structural feature of the molecule.

In other contexts, monocyclic also appears in graph theory, where a monocyclic graph is a connected graph containing exactly one cycle, reflecting the idea of a single ring in a network.

Overall, monocyclic is a basic descriptor signaling a single-ring topology, applicable to a wide range of organic compounds and related disciplines.