3.3.7 ande 3.3.8 Optical Isomerism and aldehydes and ketones Flashcards
Name the 2 types of isomerism
Structural isomerism
Stereoisomerism
Name the 3 types of structural isomerism
Positional isomerism
Chain isomerism
Functional isomerism
Name the 2 types of Stereoisomerism
Geometrical isomerism - E/Z
Optical isomerism
Structural isomerism definition
Same molecular formula but different structural formula
Stereoisomerism definition
Same structural formula
Bonds arranged differently in space
What are the key points of optical isomerism?
- Carbon centre bonded to 4 different groups (chiral centre)
- Forms 2 isomers that are mirror images (pair of enantiomers)
Non-superimposable mirror images definition
Bonds don’t line up with each other when on top of each other
What is optimal isomerism?
Optical isomers rotate a plane off polarised light, one isomer will rotate it anti clockwise, the other clockwise
Chiral definition
4 different groups on 1 carbon
Chiral centre definition
A central carbon bonded to 4 different groups
Stereogenic centre definition
A central carbon bonded to 4 different groups
Enantiomer definition
A single optical isomer
Enantiomerically pure definition
A sample with 1 optical isomer
Optically active definition
A sample with 1 optical isomer
Racemic mixture definition
A sample with both optical isomers in equal amounts
What are the properties that all optical isomers have in common?
- Melting and boiling point
- Solubility in a range of solvents
- Mr value
- Peaks in their NMR spectrum, IR and mass spectrum
What is the case study for optical isomers?
Thalidomide
Why is it not possible to produce an optically active sample?
In a lab all drugs are produced in a racemic mixture and so will rotate a plane in polarised light equally in opposite directions
Equation for an aldehyde to a primary alcohol
CH3CHO + 2[H] –> CH3CH2(OH)
Equation for a ketone to a primary alcohol
CH3C(CH3)O + 2[H] –> CH3CH(OH)CH3
What is the reagent for the reduction of aldehydes and ketones?
NaBH4 (reducing agent)
What is the mechanism for the reduction of aldehydes and ketones?
Nucleophillic addition
What is the nucleophile in the reduction of aldehydes and ketones?
Hydride
H:-
What is the condition needed for the reduction of aldehydes and ketones?
Dilute acid
Equation for the reduction of propane to propane-1-ol
CH3CH2CHO + 2[H] –> CH3CH2CH2OH
Equation for the reduction of butane to butan-2-ol
CH3CH2COCH3 + 2[H] –> CH3CH2CHOCH3
What is the reagent for the reaction of aldehydes and ketones with :CN-?
KCN and dilute HCl
What is the mechanism for the reaction of aldehydes and ketones with :CN-?
Nucleophillic addition
What is the nucleophile for the reaction of aldehydes and ketones with :CN-?
:-CN
What is the condition needed for the reaction of aldehydes and ketones with :CN-?
Acidic
What is the name of the product when aldehydes and ketones react with :-CN?
Hydroxynitriles
Why can nucleophillic addition to aldehydes and asymmetrical ketones result in a racemic mixture of optical isomers
- The bonding is about a C=O planar group in an aldehyde and ketone is planar
- This means there is a 50:50 chance of the nucleophile attacking from one side of the molecule or the other
- Resulting in equal proportions of each optical isomer, forming a racemic mixture
