3.3.7 Optical Isomerism Flashcards
What is optical isomerism?
a form of stereoisomerism and occurs as a result of chirality in molecules, limited to molecules with a single chiral centre.
What are enantiomers?
Optical isomers that have the same molecular and structural formulas, except that one is a mirror image of the other.
atoms are arranged differently in space around a chiral carbon center.
What gives rise to optical isomers?
an asymmetrical carbon atom that has a chiral center gives rise to optical isomers.
optical isomers exist as non-superimposable mirror images and differ in their effect on plane polarised light.
how does a pair of optical isomers differ?
they differ in the way they rotate a plane of polarised light.
one rotates it clockwise and the other rotates it anticlockwise.
how can we identify optical isomers?
shine plane polarised light through the two samples.
one rotates it clockwise and the other rotates it anticlockwise.
what is a racemic mixture/racemate?
a solution containing equal amounts / 50:50 mixture of +ve optical isomers and -ve isomers
the rotation is equal and opposite therefore cancels out.
why do most synthetic processes form racemic mixtures?
they are formed from nucleophilic additon reactions with alcohols
the nucleophile attacks the C=C bond which is planar
meaning it is equally like to attack either side so equal amounts of the isomer is formed.
explain why a mixture formed from a reaction of a ketone and HCN could produce such a mixture.
the HCN will attack the C=O, which is a planar carbonyl group…
so the HCN could attack either side meaning it is equally as likely for each of the isomers to be formed.
