Locants

Part of speech: noun

Definitions

1. Numbers or letters used in chemical nomenclature to show where a particular atom or group sits within a molecule's structure
2. Position markers, typically numerals or letters, that identify which atom in a compound a substituent or functional group is attached to
3. Labels in systematic chemical naming that specify the place on a ring or chain where a side group or double bond occurs

Etymology: "Locants" is the plural of "locant," a term used in chemistry to name the position of a substituent on a molecule's parent structure. Its base is the Latin "locus," meaning "place," with the suffix "-ant" added to it, so a locant is literally a place-marker. In chemical nomenclature, the numbers or letters that specify where a group attaches to a ring or chain are the locants, letting a name such as "2-chlorobutane" pinpoint exactly which carbon carries the chlorine.