optical isomerism and aldehydes and ketones

Question 1

optical isomerism - key points

Answer 1

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)

Question 2

optical isomerism

Answer 2

optical isomerism rotate the plane of polarised light
one isomer will rotate is clockwise the other will rotate it anticlockwise

Question 3

racemic mixture

Answer 3

a sample that has both optical isomers in equal amounts

Question 4

model answer - why can nucleophilic addition to aldehydes and asymmetrical ketones result in a racemic mixture of optical isomers

Answer 4

• 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.