Definition: any compound in which the constituent atoms, or any part of them, form a ring. Used mainly in organic chemistry where: 1) numerous compounds contain rings of carbon atoms (carbocyclic compounds) or carbon atoms plus one or more atoms of other types (heterocyclic compounds), usually nitrogen, oxygen, or sulfur; 2) where the atoms in the ring are all of the same element (homocyclic or isocyclic compound); 3) where the ring is saturated or contains nonconjugated double bonds (alicyclic compound), the compound is similar in properties to the corresponding acyclic compound (cyclohexane resembles hexane); 4) where the ring contains conjugated double bonds in a closed loop in which there are 4n + 2 (where n is an integer) delocalized p electrons (Hückel rule) (aromatic compound; benzene, pyridine), it is more stable than the corresponding saturated ring and exhibits unusual chemical properties characteristic of itself and not of other types of rings or of acyclic compounds. These aromatic compounds have the ability to sustain an induced ring current.
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Examples: glitazone, GI cocktail, etc.