Optical Isomerism Flashcards
What is a racemic mixture (racemate)
A mixture that contains 50:50 of two enantiomers and occurs when there is an equal chance of forming each one during the chemical reaction
What happens when plane polarised light passes through an optically active compound?
The angle of the plane is rotated either clockwise or anti-clockwise.
What is a chiral carbon?
A carbon atom bonded to four different groups. Molecules with a chiral carbon are said to have a chiral centre
Why don’t racemic mixtures rotate plane polarised light?
The enantiomers in the mixture both rotate the plane of polarised light but the rotation effects of each isomer are equal and opposite and therefore cancel out
What is optical rotation?
The degree by which the plane of polarised light is rotated when passed through an optically active compound
We often obtain racemic mixtures when we…
…addition reactions on a planar double bond (C=C or C=O), because the reaction can occur with equal probability from either side of the plane
What is optical isomerism?
A form of stereoisomerism displayed by molecules that display an asymmetric carbon atoms (one that has 4 different carbon atoms bonded to it)
What are dextrorotary and laevorotary enantiomers?
Dextrorotary - rotate plane of polarised light clockwise
Laevorotary - rotate the plane of polarised light anti-clockwise
How do the properties of enantiomers differ?
Identical physical and chemical properties apart from:
- They interact with plane polarised light differently, referred to as optical activity
- They interact differently with other asymmetric molecules, especially enzymes
Give an example of an optical isomer that interacts differently with other chiral molecules
Ibuprofen - dextrorotary isomer far more biologically active than laevorotary isomer
