3.7 Optical Isomerism
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What property must a carbon atom have for the molecule to display optical isomerism about that carbon atom?
4 different substituents attached to one carbon atom
What are the similarities and differences between two optical isomers?
Same atoms and bonds, but they are non-superimposable mirror images of one another. NOT IDENTICAL in chemical properties necessarily. Differ in the way they rotate plane polarised light- rotate plane of polarisation by the same angle but in different directions.
What word is used to describe optically active molecules?
chiral
What are the pair of isomers called?
Enantiomers
What is the chiral centre?
The carbon that has four different substituents attached to it
How is the chiral centre denoted?
C*
How is light polarised?
By passing it through a polaroid filter, so oscillations are only in one plane.
What is a structural isomer?
Same molecular formula different structures.
What can structural isomers arise from?
Chain isomers Position isomers Functional group isomers
What is a Functional group isomer?
Compounds with the same molecular formula but with atoms arranged to give different functional groups.
What is a stereoisomer?
Same structural formulae but have a different spatial arrangement of atoms
What are the two types of stereoisomers?
E-Z isomers and Optical isomers
What is a chiral (asymmetric) carbon?
A carbon that has four different groups attached
A chiral carbon has four groups arranged tetrahedrally around it, what does this cause?
Cause two different isomers that are not superimposable to be formed, which are mirror images.
What are two compounds that are optical isomers of each other called?
enatiomers
What is a racemic mixture?
A mixture containing (50/50) mixture of two isomers (enantiomers).
Page 5 3.7 chem sheets
How does a racemic mixture react with plane polarised light?
A racemic mixture will not rotate plane polarised light.
How do optical isomers react with plane polarised light?
Optical isomers have similar physical and chemical properties, but they rotate with plane polarised light in different directions. One enantiomer rotates it in one direction and the other enantiomer rotates by the same amount in the opposite direction. clockwise and anti-clockwise.
How is racemate formed?
A racemate will be formed in a reaction mechanism when a reactant or intermediate has a trigonal planar group in the molecule is approached from both sides by an attacking species.