Stereochemical Indicators

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After the ligands are ranked, an indicator is assigned as shown in the following table.¹

Stereocenter	Indicator
Double bond	Z if the highest ranking ligand of each pair are on the same side of the bond; otherwise E.
Tetrahedral atom	When the lowest-ranking ligand is located behind the central atom: · R when remaining 3 ligands are arranged clockwise in descending order · S when remaining 3 ligands are arranged counterclockwise in descending order · r or s is used for pseudoasymmetric atoms

¹R.S. Cahn, C.K. Ingold, and V. Prelog, "Specification of Molecular Chirality", Angew. Chem., Int. Ed. Engl. 1966, 5, 385-414 (errata: 1966, 5, 511); Angew. Chem. 1966, 78, 413-447.

¹V. Prelog and G. Helmchen, "Basic Principals of the CIP-System and Proposals for a Revision", Angew. Chem. 1982, 94, 614-631; Angew. Chem. Int. Ed. Engl. 1982, 21, 567-583.

¹P. Mata, A.M. Lobo, C. Marshall, and A.P. Johnson, "The CIP Sequence Rules: Analysis and Proposal for a Revision." Tetrahedron:Asymmetry. 1993, 4, 657-668.