CIP rule
CIP rule

source : Chemistry Libre Texts

   CIP rule-

 The Cahn- Ingold – Prelog (CIP) sequence rules, named for Robert Sidney Cahn, Crystopher Kelk Ingold & Vladimir Prelog -alternatively known as CIP Rule. The purpose of  CIP priority  rule is to name a specific stereoisomer of a molecule. Stereoisomers are compounds having same molecular formula and same connectivity of atoms but differ in their three dimentional orientation.

The configuration of the chiral carbon is decided as follow-

The four atoms or groups attached to the chiral carbon are ranked in order of priority , priority is decided by following sequence rules.

(a)      Atom of higher atomic number gets priority. Atom of higher priority is assigned no.1 & atom of least priority is assigned no.4.


decreasing priority

source : wikipedia

(b)      If the first atom is the two groups have same atomic number then relative priority of the group is decided by a comparison of the atomic number of the next atom in the two groups.

Ex.1—-    In CH & –CH2–CH3


In both first atom is Carbon but next atom in –– CH 3     is H , while in ––CH2––CH3 , next atom is ‘C’. So ethyl group is given higher priority than methyl group.

Ex.2 —   –CHO is given higher priority than –CN because in group image003 , C is directly attached to oxygen while in –CN group C is directly attached to N. (at. no. of oxygen is greater than N).

(c)       Multiple bonds are treated as separate single bonds.

Ex.1—-   –CH=O is given priority over –CH2OH


Examples Of  CIP rule –

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source : OChemPal

source : Chemistry for