locantn.
/ˈlɒk(ə)nt/, U.S. /ˈlɑk(ə)nt/ Chemistry.
A number or letter in the systematic designation of a compound that indicates the position in its molecular structure of a constituent atom or group.
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locant1946
1946 G. M. Dyson Lect. New Notation Org. Chem. 10 A number immediately preceding a symbol is referred to as a locant, as, for example, in ‘2ZN’ or ‘6, 7QC’; in the second example both 6 and 7 are locants.
1952 Chem. & Engin. News 2 June 2337/1 He [sc. G. M. Dyson] also thinks that a subscript might be used to indicate a number of identical locants; for example 1,1,1,2,2,3,3,4-octachloro- might be written 13,22,32,4-octachloro-.
1968 R. S. Cahn Introd. Chem. Nomencl. (ed. 3) viii. 79 Locants used for the ring system are the usual numerals—the ‘2’ in the examples above refer to the 2-position of the naphthalene nucleus.
2008 Biochemistry 47 5761 (caption) The individual amide substituents are identified by locants a–f, according to the IUPAC-IUBMB nomenclature for corrinoids.
This entry has been updated (OED Third Edition, December 2015; most recently modified version published online March 2022).
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n.1946