Exam 3

Question 1

What is enantiomeric excess

Answer 1

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

Question 2

how do you calculate enantiomeric excess

Answer 2

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

Question 3

What does FDA require for chiral drugs?

Answer 3

it requires a 100% ee of one enantiomer

Question 4

when is the enantiomeric excess 100%

Answer 4

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

Question 5

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

Answer 5

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

Question 6

what is the enantiomeric excess of a racemic mixture?

Answer 6

0%

Question 7

what is a racemic synthesis

Answer 7

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

Question 8

what is asymmetric synthesis

Answer 8

it is where one enantiomer is favored over the others

Question 9

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

Answer 9

we must separate the enantiomers

Question 10

What is a chiral resolution

Answer 10

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

Question 11

what is a chiral auxilary

Answer 11

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

Question 12

What is a chiral resolution

Answer 12

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

Question 13

what is the process of a chiral resolution

Answer 13

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

Question 15

what is the process of a chiral resolution

Answer 15

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

Question 16

What are stereoselective reactions

Answer 16

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

Question 17

what are enantioselective rxns

Answer 17

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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

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

Answer 20

it serves as a electrophile

Question 21

what classifications are important on alkyl halides

Answer 21

they can be primary, secondary or tertiary

Question 23

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

Answer 23

alkenyl halides/ vinylic halides

Question 24

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

Answer 24

aryl halides

Question 25

What is an SN reaction

Answer 25

nucleophillic substitution

Question 26

what is a nucelophile

Answer 26

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

Question 27

what is the leaving group

Answer 27

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

Question 28

what is a bimolecular rate law

Answer 28

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

the rate is dependent on both concentrations.

Question 29

what is an SN2 reaction

Answer 29

it is a concerted mechanism with inversion of all groups

it is concerted because it occurs all in one step

Question 30

what makes a good leaving group

Answer 30

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

Answer 31

it reacts with the substrate