Optical Isomers
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What is optical isomerism?
A type of stereoisomerism where molecules have the same molecular formula but a different spacial arrangement of atoms in space
Requirements for optical isomerism
An asymmetrical carbon A chiral carbon centre
What is a chiral carbon?
A carbon atom that is bonded to four different atoms or groups of atoms
What compounds are produced from optical isomerism?
Two isomers which are mirror images of another
What are the two different isomers called?
Enantiomers
Effect of plane polarised light on enantiomers
Enantiomers affect plane-polarized light by rotating it in opposite directions by 90 degrees. One enantiomer rotates the light clockwise, while the other rotates it anticlockwise.
Why are racemic mixtures optically inactive
The opposite turning rotations cancel each other out, so it does not rotate plane-polarized light
What is a racemate
When optical isomers are produced as a pair of enantiomers in a 1:1 ratio
What is a racemix mixture
An optically inactive mixture of racemates
What mechanism forms optical isomers?
Nucleophilic addition reactions
Process of a nucleophilic addition reactions in forming an optical isomer
1) A negative nucleophile attacks the C=O bond (curly arrow). 2) Electrons transferred from the middle of the double bond to O (curly arrow). This then forms a compound with the nucleophile attached and a single bond to the negative O. 3) Electrons move from the negative O to H+ ion. Forms a compound with a H attached to the O - producing an OH group.
Why are racemic mixtures formed? [3]
[1] Planar structure [2] Equal chance of being attacked from above or below [3] Giving equal chance of enantionmers forming
What are enantiomers?
Non superimposible mirror images that differ in their effect of plane polarised light
How are enantiomers drawn?
Take the chiral carbon that has the 4 groups attached Draw the tetrahedral 3D shape around the chiral carbon. Straight line up and to the left, dotted line to right, triangle down