8d Flashcards
to create stereochem what do we need
to create stereochem we need existing stereochem
aka to creat a stereogenic centre aka a chiral centre we need smt with a chiral centre
what do we count as existing stereochem
- substrate
- chiral auxiliary
- catalyst
when we want to use both enantiomers for a reaction what do we need to do
we need to form a racemix mix and then separate the enantiomers to use them
whats resolution
process of separateing enantiomers in a racemic mix
why are enantiomers difficult to separate
bc they have the same physical properties
aka the same mp, bp, solubility in all solvents and affinity for the mobile phase in chromatography
what things have different physical properties
diastereoisomers have different physical properties
how do we separate enantiomers then
we form diastereoisomers
if we have S and R mandelic acid how can we turn them into diastereoisomers
we need another chiral molecule to boind to it
aka S-alanine
they form a complex and u have SS and RS
and obvs these are diastereoisomers and therfore have different physical solubilities
aka one can dissolve but one may form a precipitate and so filtration can work to separate them
resolution has occured.
when the complex between S- alanine and the R and S mandelic acid,, does a covalent ond form
no
no covalent bond was made and this is good bc it means we then dont need to break this bond once the diastereoisomers have been made.
how do we resolute via covalnent bond
we form a covalent bond to the chiral compound were using
this is called the resoluting agent and its used to make diastereoisomers
but then we need to break the covalent bond to free the compound
whats chromatography
a purification method
diff types of chromatogrpahy
- thin layer
- paper
- high pressure
- gas
can enantiomers be separated using chromatography
nope
they have the same retention factor
how can we separate enantiomers using chromatography
we need to make diastereoisomers
we form the diastereoisomers by covalently attaching the resolving agent to the compound then separating them using chromatography.
how does column chromatography work
it works by having one enantiomer of a chiral compund in the coloumn
and then the enantiomers respond to it differently ( they respond to the columb differently)
and elute at diff rates (aka theyre washed away at diff rates)
this is used to measure enantiomer excess rather than separation
