The IUPAC rules for assigning configurations to stereogenic centers were developed by a committee consisting of Robert Cahn, Christopher Ingold, and Vladimir Prelog, and are widely known as the CIP rules. Unlike Emil Fischer's rules, still widely used in carbohydrate chemistry and biochemistry, the CIP rules assign a configuration to each individual stereocenter.

• To start, locate the stereocenters in the molecule. You are looking for atoms (not necessarily carbon) with four different ligands attached.

• Draw a stereoprojection for each stereogenic center

• Assign priority numbers, 1 - 4, to each ligand on the stereogenic center according to the following scheme:
  • Higher atomic number takes priority over lower

  • If a distinction cannot be made at the atom directly attached to the stereogenic center, move to the next atom in that ligand; continue until a distinction can be made

  • For isotopes, higher atomic mass takes priority over lower

  • Treat multiply bonded atoms as multiple atoms singly bonded; thus *C=O is treated as O-*C-O-C

• Reorient the stereoprojection so that the lowest priority ligand is directed away from you, and ignore it

• Trace the descending priority order of the remaining ligands

• If the trace moves clockwise, the configuration is R (Latin, rectus); if anticlockwise, the configuration is S (Latin, sinister)

Here are a few examples:

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