OPTICAL ISOMERS/ALDEHYDES AND KETONES Flashcards
Aldehydes —> carboxylic acid
Reaction: oxidation
Reagent: accidified potassium dicromate
Condtion: Reflux
Chemical TESTS to distinguish between aldehydes & ketones
1.
Tollen’s reagent
Aldehyde: silver mirror
Ketone: NVC
2.
Felling’s solution
Aldehyde: brick red ppt
Ketone: NVC
Why nucelophilic addition reaction of KCN, followed by dillyte acid, can produce a mixture of enantiomers (3 marks)
C=O planar
50:50 chance of nucelophile attaching from both sides
Results in equal proportions of each optical isomer formed so racemic mixture
Type of reaction that produces primary alchols from aldehydes
Reduction
Type of reaction that forms secondary alchols from ketones
Reduction
Mechanisms for:
Aldehyde ——> primary alcohols
(3marks)
Nucelophilic addition
NaBH4
Condition: acidic solvent
Mechanism for:
Ketone——>secondary alcohol
(3 marks)
Nucelophilic addition
Reagent: KCN & HCl
Condition: acidic solvent
Definition: strreoisomerism
Same structural formula different arrangement of atoms in space
What are optical isomers? (1 mark)
Non-superimposable mirror images
What is optical isomerism? (4 marks)
Molecules with chiral centres
Non-superimposable mirror images
Rotate plane of polarised light in opposite dirrection
One isomer rotates it clockwise and the other anticlockwise
How racemic mixtures are formed and why they are optically inactive (6 marks)
C=O planar
Nucleophilic artack
50:50 chance H attacking from either side
Exsists in 2 chiral form
Equal amount of enantiomer mixture formed
Optical isomers rotate plane of polarised light equally
Racemic mixture effects cancel
Chiral
Pair of optical isomers
Chiral centre
C attached to 4 different group
Enantiomer
Each optical isomer
Enantiomerically pure
Sample with 1 optical isomer
