Optical isomerism Flashcards
(14 cards)
What is a stereoisomer
Same structural formula but different arrangement of atoms in space
What are the 2 types of stereoisomerism
E-Z
Optical isomerism
Also cis-trans which is essentially just a special case of E-Z
What is the condition for optical isomerism to arise in organic compounds
The presence of a chiral carbon which gives rise to a non superimposable mirror image
What is a chiral carbon
An unsymmetric carbon
Carbon atom attached to 4 different groups
How many ways can a compound with a chiral carbon exist as
2 (2 optical isomers)
What is each isomer called for a molecule with a chiral carbon
An enantiomer
How do the 2 enantiomers which arise from a compound with a chiral carbon differ, and how are they the same
Their physical and chemical properties are identical due to the same functional group, but they differ in their ability to rotate plane polarised light
Also affect enzyme activity
What is a racemic mixture
A mixture of equal amounts of the two
optical isomers which will not rotate plane-polarised light.
How is a racemic mixture formed
The carbonyl group is planar (or any intermediate must be planar around central C if gives rise to enantiomers)
So there is an equal probability of a nucleophilic attack from either side
This leads to the formation of a racemic mixture
Give an example of how drug action is determined by the stereochemistry of a molecule
Thalidomide - the two isomers of the molecule have different effects on the body as enzymes react differently with the 2 optical isomers
What does optical activity mean
Ability to rotate plane polarised light
Why is a racemic mixture optically inactive
The different enantiomers rotate the plane of polarised light equally but in different directions and so the effects of the 2 enantiomers cancel out
What are the conditions for EZ isomerism to arise
C=C can’t rotate
Each carbon in double bond has 2 different groups attached
