Cahn-Ingold-Prelog system priority rules

CIP system (Cahn-Ingold-Prelog system) A method of producing a sequence rule used in the absolute description of stereoisomers in the R—S convention (see optical activity) or the E-Z CONVENTION. The rule is to consider the atoms that are bound directly to a chiral center (or to a double bond). The group in which this atom has the highest proton number has the highest priority. So, for example, in HCClBr(NH2), the order of priority is Br > Cl > NH2 > H. If two atoms are the same, the substituents are considered, with the substituents of highest proton... 

In the stereochemical nomenclature of coordination compounds, the procedure for assigning priority numbers to the ligating atoms of a mononuclear coordination system is based upon the standard sequence rules developed for chiral carbon compounds (the Cahn, Ingold, Prelog or CIP rules6, see Section IR-9.3.3.2). 

The absolute configuration system stems from the Cahn-Ingold-Prelog priority rules, which allow a precise description of a stereocenter without using any reference compound. In fact the basis is now the atomic number of the stereocenter substituents. 

FIGURE 1.9 cis trans (or Z/ ) stereochemistry. If a = a we use the cis/trans nomenclature, but if a a (which is the case for fatty adds because the terminus of the a group is the CH3 group and the terminus of the a group is carboxylate), we should more correctly use the Z/E system based on Cahn-Ingold-Prelog priority rules. In practice, it must be noted that most people still use the cis/treats system for the stereochemistry of fatty acids. 

Use the Cahn-Ingold-Prelog rules outlined in ChemActivity 6, Model 11. Recall that priority is assigned based on atomic number with a card game system for breaking ties (see example below). 

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