Cahn-Ingold-Prelog system rotating molecules

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 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. 

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