Exam 3 Flashcards
What is enantiomeric excess
in non-racemic mixtures, on enantiomer is more abundant than the other, the composition of this mixture is described by enantiomeric excess
how do you calculate enantiomeric excess
(moles of one enantiomer- moles of other enantiomer) / total moles X 100%
What does FDA require for chiral drugs?
it requires a 100% ee of one enantiomer
when is the enantiomeric excess 100%
when a only a single enantiomer is present, it is pure
In reactions carried out with achiral reactants, what kind of product can form and why is this a problem?
this can create chiral products, in the absence of chiral influence, the outcome of the reaction can be racemic which is a 50:50 mix of enantionmers that has a 0% enantiomeric excess
what is the enantiomeric excess of a racemic mixture?
0%
what is a racemic synthesis
it gives a 50:50 mixture where neither enantiomer is favored and gives a 0% ee
what is asymmetric synthesis
it is where one enantiomer is favored over the others
what do we do if we have to do racemic mixtures?
we must separate the enantiomers
What is a chiral resolution
Chiral resolution, or enantiomeric resolution, is a process in stereochemistry for the separation of racemic mixture into their enantiomers
what is a chiral auxilary
stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis.
What is a chiral resolution
Chiral resolution, or enantiomeric resolution, is a process in stereochemistry for the separation of racemic mixture into their enantiomers
what is the process of a chiral resolution
first the enantiomers need to be reacted with a chiral auxilary
the chiral auxilary will create two diastereomers that can be separated by conventional means
if we do a distillation, we can separate the two diastereomers into flasks and then remove the chiral auxilaries to have the two original enantiomers separated
what is the process of a chiral resolution
first the enantiomers need to be reacted with a chiral auxilary
the chiral auxilary will create two diastereomers that can be separated by conventional means
if we do a distillation, we can separate the two diastereomers into flasks and then remove the chiral auxilaries to have the two original enantiomers separated
What are stereoselective reactions
they are reactions that lead to the preferred formation of one stereoisomer over other stereoisomers
what are enantioselective rxns
rxns that favor the production of one enantiomer over its mirror image
what type of substrates are involved in substitution and elimination reactions?
alkyl halides where halogen atoms are bonded to an sp3 hybridized carbon atom
what is important about the carbon-halogen bond in an alkyl halide?
It is polarized and defined by its dipole moment where the carbon has a partial positive charge and the halogen has a partial negative charge
why is it important that the carbon has a partial positive charge in an alkyl halide?
it serves as a electrophile
what classifications are important on alkyl halides
they can be primary, secondary or tertiary
compounds in which a halogen atom is bonded to an alkene carbon are
alkenyl halides/ vinylic halides
compounds that have a halogen bonded to an aromatic ring are called
aryl halides
What is an SN reaction
nucleophillic substitution
what is a nucelophile
any negative ion or uncharged molecule with an unshared electron pair is a potential nucleophile
what is the leaving group
is always a species that takes a pair of electrons with it when it departs
what is a bimolecular rate law
the rate of the reaction is = the rate constant (K) x [substrate][nucleophile]
the rate is dependent on both concentrations.
what is an SN2 reaction
it is a concerted mechanism with inversion of all groups
it is concerted because it occurs all in one step
what makes a good leaving group
a good leaving group is a substituent that can leave as a relatively stable, weakly basic molecule or ion
it reacts with the substrate
