What does annulation mean?
Annulation is a chiefly scientific term referring to the formation of rings. In organic chemistry it denotes a reaction in which a new ring is built onto an existing molecular framework, a fundamental strategy for constructing complex molecules such as pharmaceuticals and natural products; chemists classify annulations by the size of the ring formed and often name them accordingly. In biology the word carries a related but distinct meaning: the ringed or segmented condition of an organism or body part, as seen in the banded bodies of annelid worms such as earthworms. The term derives from Latin annulus, meaning ring, via the verb anulāre, to make ring-shaped. Though rare outside technical writing, annulation is valuable vocabulary for anyone reading chemistry literature or studying comparative anatomy, and it sits comfortably alongside related terms such as cyclization and ring closure.
nounThe act or process of forming a ring, especially in chemistry the construction of a new ring onto an existing molecular structure. It can also denote a ring-shaped marking, structure, or segment, as on an animal or plant part.
- In chemistry: the formation of a new ring fused onto an existing ring system within a molecule, a key strategy in organic synthesis.
- A ring-like structure, band, or segmentation; the state of being composed of or marked with rings (as in annelid worms).
"The synthesis proceeded smoothly thanks to a highly efficient annulation step that closed the final ring."
"The Diels–Alder annulation efficiently constructed the six-membered ring at the core of the natural product."
"The earthworm's body displays clear annulation, its segments divided by shallow grooves."
Used when referring to multiple ring-forming reactions or multiple ring-like bands.
"Several successive annulations were required to assemble the polycyclic framework."
Chemists use 'annulation' to describe stitching brand-new rings onto molecules — the same word that biologists use for the banded rings on an earthworm's body.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of annulation
Annulation comes from the Latin annulus, meaning 'ring', combined with the suffix -ation to form a noun of action from the post-classical Latin anulāre, 'to make ring-shaped'. The term entered English in the 19th century, first in biology to describe ringed or segmented structures, and later became standard in organic chemistry for reactions that form new rings. It shares its root with annular (ring-shaped), annual (originally relating to yearly cycles), and annulus itself.
Related word forms
How annulation is actually used
Primarily a technical term used in organic chemistry, where it appears frequently in reaction names and synthetic planning; in zoology and botany it is rarer and describes ringed or segmented structure. Not used in everyday speech.
Easily confused with annulation
An annulment is the legal declaration that a marriage is void, whereas annulation refers to ring formation in chemistry or ring-like structures and markings in biology.