dr. wolf's chm 201 & 202 7-1 7.12 molecules with multiple chirality centers
TRANSCRIPT
7-1Dr. Wolf's CHM 201 & 202
7.127.12
MoleculesMolecules
withwith
Multiple Chirality CentersMultiple Chirality Centers
Dr. Wolf's CHM 201 & 202 7-2
maximummaximum number of stereoisomers = 2 number of stereoisomers = 2nn
where where nn = number of structural units capable of = number of structural units capable of stereochemical variationstereochemical variation
structural units include chirality centers and cis structural units include chirality centers and cis and/or trans double bondsand/or trans double bonds
number is reduced to less than 2number is reduced to less than 2nn if meso forms if meso forms are possibleare possible
How many stereoisomers?How many stereoisomers?How many stereoisomers?How many stereoisomers?
Dr. Wolf's CHM 201 & 202 7-3
ExampleExampleExampleExample
4 chirality centers4 chirality centers
16 stereoisomers16 stereoisomers
OO
HOCHHOCH22CCH—H—CCH—H—CCH—H—CCHCHHCH
OHOH OHOH OHOH OHOH
7-4Dr. Wolf's CHM 201 & 202
HOHO OHOH
HH
HH
HOHO
HH33CC
HH
HHCHCH22CHCH22COCO22HH
CHCH33
HH
CHCH33
11 chirality centers11 chirality centers
221111 = 2048 stereoisomers = 2048 stereoisomers
one is "natural" cholic acidone is "natural" cholic acid
a second is the enantiomer of a second is the enantiomer of natural cholic acidnatural cholic acid
2046 are diastereomers of cholic 2046 are diastereomers of cholic acidacid
Cholic acid Cholic acid Cholic acid Cholic acid
Dr. Wolf's CHM 201 & 202 7-5
maximummaximum number of stereoisomers = 2 number of stereoisomers = 2nn
where where nn = number of structural units capable of = number of structural units capable of stereochemical variationstereochemical variation
structural units include chirality centers and cis structural units include chirality centers and cis and/or trans double bondsand/or trans double bonds
number is reduced to less than 2number is reduced to less than 2nn if meso forms if meso forms are possibleare possible
How many stereoisomers?How many stereoisomers?How many stereoisomers?How many stereoisomers?
Dr. Wolf's CHM 201 & 202 7-6
3-Penten-2-ol3-Penten-2-ol
HOHO HH
EE RR
HH OHOH
EE SS
HHHOHO
ZZ RR
HH OHOH
SS
How many stereoisomers?How many stereoisomers?How many stereoisomers?How many stereoisomers? ZZ
7-7Dr. Wolf's CHM 201 & 202
7.13 7.13
Chemical Reactions That Chemical Reactions That
Produce Diastereomers Produce Diastereomers
7-8Dr. Wolf's CHM 201 & 202
In order to know understand stereochemistry of In order to know understand stereochemistry of product, you need to know two things:product, you need to know two things:
(1) stereochemistry of alkene (cis or trans; Z or E)(1) stereochemistry of alkene (cis or trans; Z or E) (2) stereochemistry of mechanism (syn or anti)(2) stereochemistry of mechanism (syn or anti)
Stereochemistry of Addition to AlkenesStereochemistry of Addition to AlkenesStereochemistry of Addition to AlkenesStereochemistry of Addition to Alkenes
CC CC ++ E—YE—Y CC CCEE YY
7-9Dr. Wolf's CHM 201 & 202
BrBr22
RR
SS RR
SS
mesomeso
anti addition to anti addition to transtrans-2-butene gives meso -2-butene gives meso diastereomerdiastereomer
Bromine Addition to trans-2-ButeneBromine Addition to trans-2-ButeneBromine Addition to trans-2-ButeneBromine Addition to trans-2-Butene
7-10Dr. Wolf's CHM 201 & 202
BrBr22
RR
RR SS
SS
50%50% 50%50%
Bromine Addition to cis-2-ButeneBromine Addition to cis-2-ButeneBromine Addition to cis-2-ButeneBromine Addition to cis-2-Butene
anti addition to anti addition to ciscis-2-butene gives racemic mixture -2-butene gives racemic mixture of chiral diastereomerof chiral diastereomer
++
7-11Dr. Wolf's CHM 201 & 202
RCORCO33HH
RR
RR SS
SS
syn addition to syn addition to transtrans-2-butene gives racemic -2-butene gives racemic mixture of chiral diastereomermixture of chiral diastereomer
Epoxidation of trans-2-ButeneEpoxidation of trans-2-ButeneEpoxidation of trans-2-ButeneEpoxidation of trans-2-Butene
50%50% 50%50%
++
7-12Dr. Wolf's CHM 201 & 202
RR
SS RR
SS
Epoxidation of cis-2-ButeneEpoxidation of cis-2-ButeneEpoxidation of cis-2-ButeneEpoxidation of cis-2-Butene
syn addition to syn addition to ciscis-2-butene gives meso -2-butene gives meso diastereomerdiastereomer
RCORCO33HH
mesomeso
7-13Dr. Wolf's CHM 201 & 202
Of two stereoisomers of a particular starting Of two stereoisomers of a particular starting material, each one gives differentmaterial, each one gives differentstereoisomeric forms of the productstereoisomeric forms of the product
Related to mechanism: terms such asRelated to mechanism: terms such assyn addition and anti addition refer tosyn addition and anti addition refer tostereospecificitystereospecificity
Stereospecific reactionStereospecific reactionStereospecific reactionStereospecific reaction
7-14Dr. Wolf's CHM 201 & 202
..
transtrans-2-butene-2-butene
ciscis-2-butene-2-butene
transtrans-2-butene-2-butene
ciscis-2-butene-2-butene brominationbromination antianti 22RR,3,3RR + 2 + 2SS,3,3SS
brominationbromination
epoxidationepoxidation
epoxidationepoxidation
antianti
synsyn
synsyn
mesomeso
mesomeso
22RR,3,3RR + 2 + 2SS,3,3SS
Stereospecific reactionsStereospecific reactionsStereospecific reactionsStereospecific reactions
7-15Dr. Wolf's CHM 201 & 202
A single starting material can give two or moreA single starting material can give two or morestereoisomeric products, but gives one of themstereoisomeric products, but gives one of themin greater amounts than any otherin greater amounts than any other
++
CHCH33
HH
CHCH33
HH
68%68% 32%32%
Stereoselective reactionStereoselective reactionStereoselective reactionStereoselective reaction
CHCH33
CHCH22
HH CHCH33
HH
CHCH33
HH
HH22
PtPt
7-16Dr. Wolf's CHM 201 & 202
7.14 7.14
Resolution of EnantiomersResolution of Enantiomers
Separation of a racemic mixture into its two Separation of a racemic mixture into its two enantiomeric formsenantiomeric forms
Dr. Wolf's CHM 201 & 202 7-17
enantiomersenantiomers
C(+)C(+)C(+)C(+) C(-)C(-)C(-)C(-)
StrategyStrategyStrategyStrategy
Dr. Wolf's CHM 201 & 202 7-18
enantiomersenantiomers
C(+)C(+)C(+)C(+) C(-)C(-)C(-)C(-)
2P(+)2P(+)
C(+)C(+)P(+)C(+)C(+)P(+) C(-)C(-)P(+)C(-)C(-)P(+)
diastereomersdiastereomers
StrategyStrategyStrategyStrategy
Dr. Wolf's CHM 201 & 202 7-19
enantiomersenantiomers
C(+)C(+)C(+)C(+) C(-)C(-)C(-)C(-)
2P(+)2P(+)
C(+)C(+)P(+)C(+)C(+)P(+) C(-)C(-)P(+)C(-)C(-)P(+)
diastereomersdiastereomers
C(+)C(+)P(+)C(+)C(+)P(+)
C(-)C(-)P(+)C(-)C(-)P(+)
StrategyStrategyStrategyStrategy
Dr. Wolf's CHM 201 & 202 7-20
enantiomersenantiomers
C(+)C(+)C(+)C(+) C(-)C(-)C(-)C(-)
2P(+)2P(+)
C(+)C(+)P(+)C(+)C(+)P(+) C(-)C(-)P(+)C(-)C(-)P(+)
diastereomersdiastereomers
C(+)C(+)P(+)C(+)C(+)P(+)
C(-)C(-)P(+)C(-)C(-)P(+)
P(+)P(+)
P(+)P(+)
C(+)C(+)C(+)C(+)
C(-)C(-)C(-)C(-)
StrategyStrategyStrategyStrategy
7-21Dr. Wolf's CHM 201 & 202
7.157.15Stereoregular PolymersStereoregular Polymers
atacticatactic
isotacticisotactic
syndiotacticsyndiotactic
Dr. Wolf's CHM 201 & 202 7-22
Atactic PolypropyleneAtactic PolypropyleneAtactic PolypropyleneAtactic Polypropylene
random stereochemistry of methyl groups random stereochemistry of methyl groups attached to main chain (stereorandom)attached to main chain (stereorandom)
properties not very useful for fibers etc.properties not very useful for fibers etc.
formed by free-radical polymerizationformed by free-radical polymerization
Dr. Wolf's CHM 201 & 202 7-23
Isotactic PolypropyleneIsotactic PolypropyleneIsotactic PolypropyleneIsotactic Polypropylene
stereoregular polymer; all methyl groups onstereoregular polymer; all methyl groups onsame side of main chainsame side of main chainuseful propertiesuseful propertiesprepared by coordination polymerization prepared by coordination polymerization under Ziegler-Natta conditionsunder Ziegler-Natta conditions
Dr. Wolf's CHM 201 & 202 7-24
Syndiotactic PolypropyleneSyndiotactic PolypropyleneSyndiotactic PolypropyleneSyndiotactic Polypropylene
stereoregular polymer; methyl groups alternate stereoregular polymer; methyl groups alternate side-to-side on main chainside-to-side on main chain
useful propertiesuseful properties
prepared by coordination polymerization under prepared by coordination polymerization under Ziegler-Natta conditionsZiegler-Natta conditions
7-25Dr. Wolf's CHM 201 & 202
7.167.16Chirality CentersChirality Centers
Other Than CarbonOther Than Carbon
7-26Dr. Wolf's CHM 201 & 202
SiliconSiliconSiliconSilicon
Silicon, like carbon, forms four bonds in its stable Silicon, like carbon, forms four bonds in its stable compounds and many chiral silicon compounds compounds and many chiral silicon compounds have been resolvedhave been resolved
SiSi SiSidd dd
aabb
cc
aabb
cc
7-27Dr. Wolf's CHM 201 & 202
Nitrogen in aminesNitrogen in aminesNitrogen in aminesNitrogen in amines
Pyramidal geometry at nitrogen can Pyramidal geometry at nitrogen can produce a chiral structure, but enantiomers produce a chiral structure, but enantiomers equilibrate too rapidly to be resolvedequilibrate too rapidly to be resolved
NN NN:: ::
aabb
cc
aabb
cc
very fastvery fast
7-28Dr. Wolf's CHM 201 & 202
Phosphorus in phosphinesPhosphorus in phosphinesPhosphorus in phosphinesPhosphorus in phosphines
Pyramidal geometry at phosphorus can produce a Pyramidal geometry at phosphorus can produce a chiral structure; pyramidal inversion slower than chiral structure; pyramidal inversion slower than for amines and compounds of the type shown have for amines and compounds of the type shown have been resolvedbeen resolved
PP PP:: ::
aabb
cc
aabb
cc
slowslow
7-29Dr. Wolf's CHM 201 & 202
Sulfur in sulfoxidesSulfur in sulfoxidesSulfur in sulfoxidesSulfur in sulfoxides
Pyramidal geometry at sulfur can produce a chiral Pyramidal geometry at sulfur can produce a chiral structure; pyramidal inversion is slow and structure; pyramidal inversion is slow and compounds of the type shown have been resolvedcompounds of the type shown have been resolved
SS SS:: ::
aabb
O_O_
aabb
O_O_
slowslow
++ ++
Dr. Wolf's CHM 201 & 202 7-30
End of Chapter 7