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For double bonded molecules, Cahn–Ingold–Prelog priority rules (CIP rules) are followed to determine the priority of substituents of the double bond. If both of the high priority groups are on the same side of the double bond (cis configuration), then the stereoisomer is assigned the configuration Z (zusammen, German word meaning "together").
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.
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]
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]
Robert Sidney Cahn (9 June 1899 – 15 June 1981) was a British chemist, best known for his contributions to chemical nomenclature and stereochemistry, particularly by the Cahn–Ingold–Prelog priority rules, which he proposed in 1956 with Christopher Kelk Ingold and Vladimir Prelog. [1] Cahn was the first to report the structure of ...
A face is labeled re if, when looking at that face, the substituents at the trigonal atom are arranged in increasing Cahn-Ingold-Prelog priority order (1 to 2 to 3) in a clockwise order, and si if the priorities increase in anti-clockwise order; note that the designation of the resulting chiral center as S or R depends on the priority of the ...
Vladimir Prelog ForMemRS [1] (23 July 1906 – 7 January 1998) was a Croatian-Swiss organic chemist who received the 1975 Nobel Prize in chemistry for his research into the stereochemistry of organic molecules and reactions. Prelog was born, and spent his infancy, in Sarajevo, and youth in Zagreb, Osijek and Prague. [3]
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 ...