Optical isomers, aldehydes + Ketones (P2+P3)
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What is optical isomerism?
• shine plane polarised light • one isomer will rotate clockwise and one isomer will rotate anti clockwise
When does optical isomerism occur?
when a carbon atom is bonded to 4 different groups
When does optical isomerism occur?
when a carbon atom is bonded to 4 different groups
What are enantiomers?
each optical isomer
What does optically active mean?
plane polarised light will rotate in one direction only.
What does optically inactive mean?
plane polarised light will rotate in opposite directions.
What is a racemic mixture?
Where equal amount of enantiomers are formed
Name the mechanism, reagents and conditions of reducing propanal to Propan-1-ol and state the equation (same mechanism for ketone to secondary alcohol)
Nucleophilic addition reagent: NaBH4 nucleophile: H:- conditions: acidic solvent CH3CH2CHO + 2[H] –> CH3CH2CH2OH
Name the mechanism, reagents and conditions of reacting propanal or propanone with KCN state the equation for propanal with KCN and name the product
Nucleophilic addition reagent: KCN OR HCl nucleophile: -:CN conditions: acidic solvent CH3CH2CHO + -:CN + H+ –> CH3CH2CH(CN)(OH) Name of product: 2-hydroxybutanenitrile
Why can a nucleophilic addition to aldehydes and ketones result in a racemic mixture of optical isomers?
bonding in C=O is planar 50/50 chance of nucleophile attacking on both sides of the molecule equal proportions of enantiomers are formed resulting in a racemic mixture.
Why is HCl not used in the reaction with aldehydes and ketones?
HCl is a weak acid so slightly dissociates into H+ ions whereas KCN fully dissociates in water so more cyanide forms