4.1 - Stereoisomerism

Structural isomerism

Structural isomers = compounds with the same molecular formula but a different structural formula

Stereoisomerism

Occurs in compounds that have the same structural and molecular formulae, but which have a different 3D arrangement of their atoms in space

Two types of stereoisomerism

E-Z and optical

How E-Z isomerism occurs

• C=C must be present

• Carbon atoms at both ends of the double bond both have two different groups bonded to them

Z isomers

Higher priority groups on same side

E isomers

Higher priority groups on opposite sides

Where optical isomerism occurs

In molecules with a chiral centre

Chiral centre

Asymmetric tetrahedral carbon atom with four different atoms/groups attached to it

Enantiomers

Pair of optical isomers which are non-superimposable images of each other

Optically active

Rotate the plane of polarised light in opposite directions

Racemic mixture/racemate

An equimolar mixture of the two optical isomers which will be optically native as the plane of polarised light is not rotated