Cahn-Ingold-Prelog system chiral molecules

Following the Cahn-Ingold-Prelog system, it is now possible to draw the structures of (i )- and (5)-enantiomers of various chiral molecules, for example 2,3-dihydroxypropanoic acid, where the priorities are 1 = OH, 2 = COOH, 3 = CH2OH and 4 = H. 

The Cahn-Ingold-Prelog rules work for inorganic compounds too but coordination complexes often have coordination numbers greater then four and may exhibit helical chirality, for example, denoted A and A (or Pand Min the Cahn-Ingold-Prelog system). The formal condition for chirality is that the molecule should not have an improper axis of rotation (i.e. a rotation + reflection axis, 5n =... 

The Cahn-Ingold-Prelog (CIP) rules stand as the official way to specify chirahty of molecular structures [35, 36] (see also Section 2.8), but can we measure the chirality of a chiral molecule. Can one say that one structure is more chiral than another. These questions are associated in a chemist s mind with some of the experimentally observed properties of chiral compounds. For example, the racemic mixture of one pail of specific enantiomers may be more clearly separated in a given chiral chromatographic system than the racemic mixture of another compound. Or, the difference in pharmacological properties for a particular pair of enantiomers may be greater than for another pair. Or, one chiral compound may rotate the plane of polarized light more than another. Several theoretical quantitative measures of chirality have been developed and have been reviewed elsewhere [37-40]. 

In response to this nomenclature dilemma, the Cahn-Ingold-Prelog (IUPAC, International Union of Pure and Applied Chemistry) system of nomenclature was developed and is now the standard mediod to specify the relative configuration of chiral centers in molecules. Each chiral center will have two possible mirror-image configurations, which are designated as eidter R or S. 

The Cahn-ingold-Prelog (CiP) system for describing the stereochemistry of chiral molecules is universally accepted.Simple molecules containing one chiral centre... 

The chirality, or handedness, of a molecule is described by specifying its configuration. The system that has received general acceptance is the Cahn-Ingold-Prelog convention, which uses the descriptors R and 5. The Fischer convention. 

In this chapter you learned how to give unique names to chiral molecules using the Cahn-Ingold-Prelog / ,5-system. You have also exercised your mind s eye in visualizing molecular structures in three dimensions, and you have refined your skill at drawing three-dimensional molecular formulas. You learned that pairs of enantiomers have identical physical properties except for the equal and opposite rotation of plane-polarized light, whereas diastere-omers have different physical properties from one another. Interactions between each enantiomer of a chiral molecule and any other chiral material lead to diastereomeric interactions, which lead to different physical properties that can allow the separation of enantiomers. 

The use of a reference axial system, whether right- or left-handed, is completely analogous to the Cahn, Ingold, and Prelog convention (75-77) regarding the specification of the absolute configuration of chiral molecules R and S as depicted in Scheme 11 for molecules with large (L), medium (M), and small... 

The sequence rule was introduced by Cahn, Ingold and Prelog (1956) as an aid to nomenclature of optically active molecules. The authors stated that use of the symbols (R) and (S) would remedy ambiguities that arose when the D and L system was applied outside the carbohydrate and amino-acid series. They also claimed that it would systematize the storage of stereochemical information and assist retrieval, e.g. for building a molecular model. The utility of the system is greatest when two or three chiral atoms are present in the same molecule. A simplified version of the sequence rule is presented by Cahn (1964). 

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