Isomerism
Structural Isomers:
Molecules that share the same molecular formula but have different structural formulae.
• Chain – different arrangement of same carbon skeleton
• Position – functional group in different placement
• Functional – different functional groups
Stereoisomerism:
Stereoisomers have the same structural formulae, but their atoms take up different arrangements in space
• Geometric / E/Z
• Optical
Geometric Isomerism:
Geometric isomers occur in molecules where there is restricted rotation around a double bond. This locks the groups
either side of the C=C bond in position.
Cahn-Ingold-Prelog (CIP) Rule
The E/Z system works by assigning relative priority to the 2 groups on each carbon of the double bond.
1. Rank the atoms attached directly to each carbon atom in the double bond based on largest atomic number.
2. If the first atoms are identical, then rank the 2nd, 3rd, 4th, etc. until a difference is found.
E = Opposite Z = Together
3
Structural Isomers:
Molecules that share the same molecular formula but have different structural formulae.
• Chain – different arrangement of same carbon skeleton
• Position – functional group in different placement
• Functional – different functional groups
Stereoisomerism:
Stereoisomers have the same structural formulae, but their atoms take up different arrangements in space
• Geometric / E/Z
• Optical
Geometric Isomerism:
Geometric isomers occur in molecules where there is restricted rotation around a double bond. This locks the groups
either side of the C=C bond in position.
Cahn-Ingold-Prelog (CIP) Rule
The E/Z system works by assigning relative priority to the 2 groups on each carbon of the double bond.
1. Rank the atoms attached directly to each carbon atom in the double bond based on largest atomic number.
2. If the first atoms are identical, then rank the 2nd, 3rd, 4th, etc. until a difference is found.
E = Opposite Z = Together
3
