Optical isomerism Flashcards
a2 chem
Optical isomerism meaning
Optical isomerism is a form of stereoisomerism, they have the same structural formula but different arrangement of atoms in space.
Describe optical isomers..
Optical isomers are mirror images of each other and have a chiral carbon atom.
What is a chiral molecule?
A chiral molecule has 4 different groups attached to a carbon atom.
We can arrange these groups in 2 ways which forms 2 different molecules known as ENANTIOMERS.
Enantiomer meaning..
Enantiomers are mirror images of each other and are non-superimposable. No matter which way you turn they won’t overap.
How to draw enantiomers?
Identify a chiral center ( carbon with 4 groups surrounding)
Then draw it into a tetrahedral 3D shape.
What are molecules with a chiral centre considered to be?
Optically active,
Optically active isomers will rotate plane polarised light. This is a method of detecting an optically active compound.
How can plane polarised light be used to detect optically active compound?
Standard light oscillates in all directions
Optically active compounds will rotate plane polarised light.
We pass the light though a polaroid filter to produce plain polarised light.
This light only oscillates in one direction.
One enantiomer rotates light clockwise, the other will rotate it anticlockwise
What is a racemic mixture?
When we have an equal amount of each enantiomer we have a racemic mixture.
Describe racemates..
Racemates do not rotate plane polarised light. The 2 enantiomers rotate light in opposite directions and they cancel out.
How can racemic mixture of a chiral product be made?
It can be made by reacting chiral substances together. When the molecules react there is an even chance of forming each enantiomer, there is a 50/50 chance
What type of molecules make racemic products?
Molecules with planar profiles such as double bonds in c=c and c=o can make racemic products.
When do reactions where racemic mixtures occur and why?
These reactions occur when we have an attack on the carbonyl group c=o of unsymmetrical ketones or aldehydes.
They occur as the c=o part of the molecule is planar there is an even chance of the nucleophile attacking from either above or below forming 2 different enantiomers.
