13.2: STEREOISOMERISM

What are stereoisomers

Compounds with the same structural formula but a different arrangement of the atoms in space.

2 Types of Stereoisomerism

1. E/Z isomerism

2. Optical isomerism

Where does E/Z isomerism occur

Only in compounds with a C=C double bond

Where does optical isomerism occur

It can occur in a much wider range of compounds including alkanes with no functional groups

Why does stereoisomerism occur around double bonds

Rotation about the double bond is restricted and the groups attached to each C atom are therefore fixed relative to each other

Why is the double bond rigid

Due to the position of the pi bond's electron density above and below the plane of the sigma bond

What 2 things must a molecule satisfy in order to have E/Z isomerism

1. a C = C double bond

2. different groups attached to each carbon of the double bond

E isomer

the isomer with the high-priority groups on opposite sides of the double bond

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Z isomer

the isomer with the high-priority groups on the same side of the double bond

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What is Cis-trans isomerism

A special case of E/Z isomerism in which two of the substituent groups are the same

Cahn-Ingold-Prelog rules

The atom which has the higher atomic number is given the higher priority.

-If the groups of higher priority are on the same side of the double bond the compound is the Z isomer

-If the groups of higher priority are diagonally placed across the double bond the compound is the E isomer