(chemistry) any of a class of compounds having five-membered ring heterocycles (or their benzo derivatives) which possess a sextet of π-electrons in association with the atoms comprising the ring, but which cannot be represented by any one covalent or polar structure; typically the ring structure contains both positive and negative delocalised charges which cannot be associated with any one ring atom, and the negative charge can also be associated with a conjugated exocyclic atom (typically oxygen, sulfur, or nitrogen).

(organic chemistry) Any compound which exhibits aromaticity.

(obsolete, organic chemistry) Synonym of oxime

(chemistry) a macrocycle

(organic chemistry) Any cyclophane in which the para positions of a benzene ring are connected by a bridge of at least 10 atoms.

(chemistry) Any compound containing a cation of general formula R₄As⁺; the arsenic analogue of quaternary ammonium compounds.

(chemistry) any polycyclic compound having the form of a cage

(chemistry) Any compound having two or more rings interconnected like the links of a chain, without a covalent bond.

(chemistry) any compound of general formula RN=N-NR₂ where not all R = H

(chemistry) any compound of general formula R₂C=N⁺=N⁻