In chemistry, congeners are chemical substances "related to each other by origin, structure, or function".[1]
Common origin and structure
Any significant quantity of a polyhalogenated compound is by default a blend of multiple molecule types because each molecule forms independently, and chlorine and bromine do not strongly select which site(s) they bond to.
Polychlorinated biphenyls (PCBs) are a family of 209 congeners.
Congeners refer to the various oxidation states of a given element in a compound. For example, titanium(II) chloride (titanium dichloride), titanium(III) chloride (titanium trichloride), and titanium(IV) chloride (titanium tetrachloride) may be considered congeners.
Congeners can refer to other elements in the same group in the periodic table. For example, congeners of the Group 11 element copper are silver and gold, sometimes found together in the same ores (porphyry copper deposit) due to their chemical similarity.