congener

Congener is a term used in chemistry and related fields to denote a compound that belongs to the same family as another, sharing a core structure or origin but differing in substituents, oxidation state, or degree of substitution. The plural congeners refers to the related members within a group. The word comes from Latin congener, meaning “of the same kind.”

In practice, congeners are used to describe complex mixtures where many related substances coexist. This is common for polychlorinated biphenyls (PCBs), dioxins, furans, and various polycyclic aromatic hydrocarbons (PAHs). Each congener has a unique arrangement of substituents or chlorine atoms and can exhibit different physical, chemical, and toxicological properties. For PCBs, there are 209 possible biphenyl congeners defined by chlorine substitution patterns, and regulatorily important analyses often report congener-specific concentrations or profiles.

In biology, congener can refer to a member of the same genus, i.e., a closely related species within a genus. More generally, it can denote a person or thing of the same kind or category as another.

Congeners are distinct from isomers, which have the same molecular formula but different structures, and from homologues, which differ by a repeating unit in a series. The concept helps scientists categorize and compare related compounds or organisms, assess cumulative or differential effects, and interpret environmental and toxicological data.