3.3.7 Optical Isomerism Flashcards
What is a racemic mixture?
A mixture of equal amounts of enantiomers
Also called racemate
What is a chiral centre?
A carbon that has four different functional groups
What can chiral molecules never do?
Superimpose
What is stereoisomerism?
Where two or more compounds have the same structural formula
They differ in the arrangement of the bonds in space
Two types: EZ and optical
What is the name for optical isomers?
Enantiomers
They are either left (S) or right handed (R)
What are optical isomers?
Where molecules with a chiral centre cannot be superimposed
How do you work out whether a chiral molecule is left or right handed?
If priority decreases clockwise, it is right handed and represented by +
If priority decreases anticlockwise, it is left handed and represented by -
Of carboxylic acids and CH3 groups, which is less important
Carboxylic acids
Are there any differences between enantiomers?
They may have different biological functions
The tend to have very similar chemical and physical properties
What are the properties of structural isomers?
Have different functional groups
Or have functional groups attached to the main chain at different points
Or have a different arrangement of carbon atoms in the skeleton of the molecule
See card
How do optical isomers occur?
When there are four different substituents attached to one carbon atom
This results in two isomers that are non-superimposable mirror images of one another, but are not identical
(Flip the horizontal groups)
What is the adjective for a compound displaying optical isomerism?
Chiral
How do you represent a chiral centre?
- next to the carbon
How does light become vertically polarised?
Light consists of vibrating electric and magnetic fields at right angles to the direction of the wave
The light passes through a special filter called a polaroid
All the vibrations are cut out except those in the vertical plane
How can optical rotation be measures using a polarimeter?
Polarised light is passed through two solutions of the same concentration, each containing a different optical isomer of the same substance
One solution will rotate the plane of polarisation through a particular angle, clockwise. This is the + isomer
The other will rotate the plane of polarisation of the same angle, anticlockwise. This is the - isomer
