Stereoisomerism

Isomers

Compounds with the same molecular formula but different arrangements of atoms. The existence of isomers is called isomerism.

Structural isomers

Compounds with the same molecular formula. but with different structural formulae.

Stereoisomers

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

E isomer

Atoms with higher atomic numbers are on opposite sides of c=c double bond. 

Z isomer

Atoms with higher atomic numbers are on same sides of c=c double bond. 

Chiral atom

Saturated carbon atoms that has four different atoms or groups attached to it.

Optically active

They rotate the plane of polarised light in opposite directions.

(-) enantiomer

Will rotate plane or plane polarised light to the left

(+) enantiomer

Will rotate plane or plane polarised light to the right

Racemic mixture

Will show no rotation of the plane of plane polarised light - it is optically inactive. The enantiomers are in equal amounts.

Test to distinguish between optical isomers. 

• ordinary light passed through a polariser generating polarised light. 

• The light enters the sample cell. If the sample has enantiomers, it will rotate the plane of plane polarised light. 

• The polarised filter is rotated until the maximum amount of light is observed. 

• The polarised filter is rotated until the maximum amount of light is observed.

• The angle through the filter was rotated is the measured angle of rotation - Revealing the direction and magnitude of the samples optical activity.