optical isomerism and aldehydes and ketones
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optical isomerism - key points
carbon centre with 4 different groups bonded -chiral centre -forms 2 isomers - mirror images - pair of enantiomers they are non-superimposable mirror images ( no matter how much you rotate you can never get the bonds to line up)
optical isomerism
optical isomerism rotate the plane of polarised light one isomer will rotate is clockwise the other will rotate it anticlockwise
racemic mixture
a sample that has both optical isomers in equal amounts
model answer - why can nucleophilic addition to aldehydes and asymmetrical ketones result in a racemic mixture of optical isomers
• the bonding is about a c=o groups in an aldehyde/ketone is planar -this means that there is a 50/50 chance of the nucleophile attacking from either side of the molecule -this results in equal proportions of each optical isomer forming so a racemic mixture is formed -a racemic mixture is not optically active as the different isomers rotate the polarised light in opposite directions equally.