Sequence Rule For assigning Chiral Configurations
Assign sequence priorities to the four substituents by looking at the atoms attached directly to the chiral center.
For example, H? < C? < N? < O? < Cl?. (Different isotopes of the same element are assigned a priority according to their atomic mass.)
2. If two substituents have the same immediate substituent atom,
evaluate atoms progressively further away from the chiral center until a difference is found.
For example, CH3? < C2H5? < ClCH2? < BrCH2? < CH3O?.
3. If double or triple bonded groups are encountered as substituents, they are treated as an equivalent set of single-bonded atoms.
For example, C2H5? < CH2=CH? < HC?C?
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