Substituents priority assignment

The enolate oxygen is always taken as a high-priority substituent in assigning the E- or Z-configuration. 

Mentally move from substituent priority 1 to 2 to 3. If you are moving in a clockwise manner, assign the label R to the chiral centre if you are moving in an anticlockwise manner, assign the label 5 to the chiral centre. 

Locate chirality centers, assign priorities to substituents, and assign R,S designations to chirality centers. 

In our discussion, C, will refer to the acetylenic carbon attached to the substituent of higher priority the other carbon is Cp. Priority assignments are made in the same manner as for R, S and E, Z specifications. 

Both the chirality of an atom and the cis-trans isomerism about a double bond can be determined by using a set of rules developed by and adopted by lUPAC [43]. These rules govern the sequencing of substituents about the chiral atom or double bond. Once the substituents are assigned a priority, simple geometric algorithms determine which type of isomerism is present These same rules are used to determine the prochirality of an atom. 

Locate the stereocenter, identify its four substituents, and assign a priority from 1 (highest) to 4 (lowest) to each substituent. 

A new rule is needed examine each substituent atom by atom until a point of difference is found that allows priority assignment based on the atomic mass of the highest priority attached atom. For 16, the analysis continues further down each carbon chain. In the chloropropyl fragment, the next carbon in the chain has the substitution pattern whereas the... 

Assign Cahn-Ingold-Prelog priorities to the following sets of substituents ... 

Step 1 Assign priorities to the four substituents in the usual way. 

Follow the steps in the text. (1) Assign priorities to the four substituents on the chiral carbon. (2) Manipulate the Fischer projection to place the group of lowest priority at the top by carrying out one of the allowed motions. (3) Determine the direction 1 —> 2 — 3 of the remaining three groups. 

Cahn-Ingold-Prelog sequence rules (Sections 6.5, 9.5) A series of rules for assigning relative priorities to substituent groups on a double-bond carbon atom or on a chirality center. 

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