Chirality 1+2 Flashcards
What are stereoisomers?
- same molecular formula but different spatial arrangements
What are diastereomers ?
- Stereoisomers that are not mirror images of eachother
What are enantiomers ?
- Nonsuperimposable mirror images of each other
Features of constitutional isomerism?
- Same formulae but different connectivity (structural) isomers
- different chemical+ physical properties
- can not interconvert
What is geometric isomerism?
- Cis and trans isomers
- same group on either side
What are the CIP rules ?
- Prioritise according to atomic number
- same side = Z , opposite = E
Are stereoisomers interconvertible?
- Not interconvertible
What is a chiral carbon?
- usually sp 3 hybridised
- has 4 different groups attached to it
- form enantiomers
What is the R configuration?
- clockwise order
- lowest priority group 4 should be going away from you - on dash bond
What is the S configuration?
- priorities move in anti-clockwise order - number 4 at back on dashed bond
What do we do if priority atom 4 not at back?
- assign chirality as usual then reverse answer
Similarities of R and S isomers
- identical physical + chemical properties
- eg.pka, bp,mp, solubility
What is an achiral carbon ?
- superimpossible
What do wedge bonds do ?
- approach you
What are L amino acids ?
- amine group is on the left
What is D amino acid ?
- amine group to the right
What is L glucose ?
- OH group to the left
What is D glucose ?
- OH to the right
What is a erythro enantiomer?
- same group on same side on Fischer projection
What is a threo enantiomers?
- same group on opposite sides on Fischer projection
2 differences in properties of enantiomers ?
- rotation of plane polarised light (PPL)
- interaction with other chiral molecules
What is plane polarised light?
- Produced by passing light through a polarising filter
- rotation of PPL measured in degrees
Rotation of PPL by enantiomers
- enantiomers rotate the plane of the PPL by equal amounts but in opposite directions
What is an enantiomeric excess ?
- Amount of pure enantiomer in excess of the racemic mixture
Enantiomers Interaction with Other Chiral molecules
- (R)-enantiomer active binds
correctly to receptor to trigger
response - (S)-enantiomer cannot bind
correctly, does not trigger
response
What is a meso compound?
- molecule has an internal plane of symmetry so its achiral
what are the equations to enantiomeric excess ?
- % enantiomeric excess = moles of one enantiomer - mole of other enantiomer / total moles of both enantiomers X 100
- % enantiomeric excess = observed specific rotation / specific rotation of pure enantiomer X 100
