https://doi.org/10.1351/goldbook.L03423
Stereodescriptors of @[email protected] with two @[email protected] When the two @[email protected] elements are both R or both S the @[email protected] is described as having an l relationship (l = like), when one @[email protected] 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 @[email protected] elements whereby the l, u relationships of the @[email protected] elements are considered in pairs.