4.1 Stereoisomerism

Stereoisomers

Molecules that have the same molecular formula but a different spatial arrangement of atoms

E/Z isomerism

Limited rotation around a C=C double bond means that priority groups of the molecule can be on the same or opposite side

E isomer

Functional groups on opposite sides

Z isomer

Functional groups on the same side

Priority rules

The higher the Ar of the group the higher its priority

The highest priority groups determine if its an E/Z isomer

Optical isomerism

A type of stereoisomerism where molecules contain a chiral centre

Chiral centre

A carbon atom with 4 different groups bonded around it

Enantiomers

2 possible isomers that are mirror images of eachother
These are optical isomers

Optical activity

Optical isomers rotate plane polarised light
Each enantiomer rotates light in the opposite direction

Racemic mixture

Contains equal quantities of each enantiomer from an optically active compound

Why is a racemic mixture optically inactive

The rotational effect on polarised light caused by each enantiomer cancels out

How are racemic mixtures produced

Nucleophillic addition reactions

Since the reaction can occur from either side of the carbonyl group it leads to the formation of both enantiomers in equal proportions, resulting in a racemic mixture