Exam 3 Flashcards

1
Q

What is enantiomeric excess

A

in non-racemic mixtures, on enantiomer is more abundant than the other, the composition of this mixture is described by enantiomeric excess

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2
Q

how do you calculate enantiomeric excess

A

(moles of one enantiomer- moles of other enantiomer) / total moles X 100%

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3
Q

What does FDA require for chiral drugs?

A

it requires a 100% ee of one enantiomer

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4
Q

when is the enantiomeric excess 100%

A

when a only a single enantiomer is present, it is pure

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5
Q

In reactions carried out with achiral reactants, what kind of product can form and why is this a problem?

A

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

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6
Q

what is the enantiomeric excess of a racemic mixture?

A

0%

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7
Q

what is a racemic synthesis

A

it gives a 50:50 mixture where neither enantiomer is favored and gives a 0% ee

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8
Q

what is asymmetric synthesis

A

it is where one enantiomer is favored over the others

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9
Q

what do we do if we have to do racemic mixtures?

A

we must separate the enantiomers

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10
Q

What is a chiral resolution

A

Chiral resolution, or enantiomeric resolution, is a process in stereochemistry for the separation of racemic mixture into their enantiomers

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11
Q

what is a chiral auxilary

A

stereogenic group or unit that is temporarily incorporated into an organic compound in order to control the stereochemical outcome of the synthesis.

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12
Q

What is a chiral resolution

A

Chiral resolution, or enantiomeric resolution, is a process in stereochemistry for the separation of racemic mixture into their enantiomers

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13
Q

what is the process of a chiral resolution

A

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

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14
Q
A
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15
Q

what is the process of a chiral resolution

A

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

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16
Q

What are stereoselective reactions

A

they are reactions that lead to the preferred formation of one stereoisomer over other stereoisomers

17
Q

what are enantioselective rxns

A

rxns that favor the production of one enantiomer over its mirror image

18
Q

what type of substrates are involved in substitution and elimination reactions?

A

alkyl halides where halogen atoms are bonded to an sp3 hybridized carbon atom

19
Q

what is important about the carbon-halogen bond in an alkyl halide?

A

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

20
Q

why is it important that the carbon has a partial positive charge in an alkyl halide?

A

it serves as a electrophile

21
Q

what classifications are important on alkyl halides

A

they can be primary, secondary or tertiary

22
Q
A
23
Q

compounds in which a halogen atom is bonded to an alkene carbon are

A

alkenyl halides/ vinylic halides

24
Q

compounds that have a halogen bonded to an aromatic ring are called

A

aryl halides

25
Q

What is an SN reaction

A

nucleophillic substitution

26
Q

what is a nucelophile

A

any negative ion or uncharged molecule with an unshared electron pair is a potential nucleophile

27
Q

what is the leaving group

A

is always a species that takes a pair of electrons with it when it departs

28
Q

what is a bimolecular rate law

A

the rate of the reaction is = the rate constant (K) x [substrate][nucleophile]

the rate is dependent on both concentrations.

29
Q

what is an SN2 reaction

A

it is a concerted mechanism with inversion of all groups

it is concerted because it occurs all in one step

30
Q

what makes a good leaving group

A

a good leaving group is a substituent that can leave as a relatively stable, weakly basic molecule or ion

31
Q
A

it reacts with the substrate

32
Q
A