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In red is the substituent which determines the final priority. In organic chemistry, the Cahn–Ingold–Prelog (CIP) sequence rules (also the CIP priority convention; named after Robert Sidney Cahn, Christopher Kelk Ingold, and Vladimir Prelog) are a standard process to completely and unequivocally name a stereoisomer of a molecule.
The designations are based on the same Cahn–Ingold–Prelog priority rules used for tetrahedral stereocenters. [3] The chiral axis is viewed end-on and the two "near" and two "far" substituents on the axial unit are ranked, but with the additional rule that the two near substituents have higher priority than the far ones. [4]
Absolute configuration uses a set of rules to describe the relative positions of each bond around the chiral center atom. The most common labeling method uses the descriptors R or S and is based on the Cahn–Ingold–Prelog priority rules. R and S refer to rectus and sinister, Latin for right and left, respectively.
Printable version; Page information; Get shortened URL; ... Figure for explanation of Cahn-Ingold-Prelog priority rule. Date: August 2006: Source: Selfmade with ChemDraw.
Alternately, all four groups can be ranked by Cahn–Ingold–Prelog priority rules, with overall priority given to the two groups on the "front" atom of the Newman projection. The two configurations determined in this way are termed R a and S a, in analogy to the traditional R/S for a traditional tetrahedral stereocenter. [12]
In general the D/L system of nomenclature is superseded by the Cahn-Ingold-Prelog (CIP) rule to describe the configuration of a stereogenic/chiral center. In the CIP or R/S convention, or sequence rule, the configuration, spatial arrangements of ligands/substituents around a chiral center, is labeled as either "R" or "S".
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See: Cahn–Ingold–Prelog priority rules Configuration assignment of the stereo center "X", the substituents are decreasingly prioritized from "A" → "D" according to the CIP rules. The stereochemical descriptors ( R ) (from Latin rectus = right) and ( S ) (from lat. sinister = left) [ 36 ] are used to describe the absolute configuration of ...