Term: l, u
https://doi.org/10.1351/goldbook.L03423

Definition:
Stereodescriptors of diastereoisomers with two chirality elements. When the two chirality elements are both R or both S the molecular entity is described as having an l relationship (l = like), when one chirality elements is R and the other S the molecular entity is described as having a u relationship (u = unlike). The notation can be extended to molecules with more than two chirality elements whereby the l, u relationships of the chiral elements are considered in pairs.

Related Terms:
1) diastereoisomers (http://doi.org/10.1351/goldbook.D01679).
2) chirality element (http://doi.org/10.1351/goldbook.C01061).
3) molecular entity (http://doi.org/10.1351/goldbook.M03986).
4) chirality (http://doi.org/10.1351/goldbook.C01058).
5) chiral (http://doi.org/10.1351/goldbook.C01057).

Source: PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2211 (https://doi.org/10.1351/pac199668122193)

Citation: '<i>l</i>, <i>u</i>' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.L03423

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