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7/24/2019 CHEM 212 - Chirality % Optical Rotation Review
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IntroductoryOrganicChemistry
Chem 212&Chem 211
Dr.LauraPavelkaDepartmentofChemistry
Pulp&Paper104
ORGANICBITES3:CHIRALITY&OPTICALROTATION
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CHEM212/211 OrganicBites3 Chapter5 3
MAKESUREYOUKEEPALLYOURISOMERS
STRAIGHT!
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StructuralIsomers
CHEM212/211 OrganicBites3 Chapter5 4
ISOMERS differentcompoundswiththesamemolecularformulaSTRUCTURAL differentconnectivity(differentnames)
STEREOISOMERS sameconnectivity,differentorientationinspace
STRUCTURALISOMERS
CH3(CH2)3CH3 PENTANE C5H12 bp =36C
CH3CH2CH(CH3)2 ISOPENTANE bp =28C
CH3C(CH3)3 NEOPENTANE bp =10C
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Stereoisomers
CHEM212/211 OrganicBites3 Chapter5 5
ISOMERS differentcompoundswiththesamemolecularformulaSTRUCTURAL differentconnectivity
STEREOISOMERS sameconnectivity,differentorientationinspace
STEREOISOMERS
trans2,3dichloro2hexene cis2,3dichloro2hexene
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Stereoisomers
CHEM212/211 OrganicBites3 Chapter5 6
ISOMERS differentcompoundswiththesamemolecularformulaSTRUCTURAL differentconnectivity
STEREOISOMERS sameconnectivity,differentorientationinspace
STEREOISOMERS
trans1,3dichlorocyclohexane cis1,3dichlorocyclohexane
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Conformers
CHEM212/211 OrganicBites3 Chapter5 7
CONFORMERS rotationalisomers
ISOMERS differentcompoundswiththesamemolecularformulaSTRUCTURAL differentconnectivity
STEREOISOMERS sameconnectivity,differentorientationinspace
*CONFORMERSARENOTTRUEISOMERS ONLYDIFFERENT
REPRESENTATIONSOFTHESAMECOMPOUND*
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ResonanceStructures
CHEM212/211 OrganicBites3 Chapter5 8
RESONANCESTRUCTURES 2+Lewisstructurestorepresentthesamemolecule
ISOMERS differentcompoundswiththesamemolecularformulaSTRUCTURAL differentconnectivity
STEREOISOMERS sameconnectivity,differentorientationinspace
*RESONANCESTRUCTURESARENOTISOMERS ONLY
DIFFERENTREPRESENTATIONSOFTHESAMECOMPOUND*
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CHEM212/211 OrganicBites3 Chapter5 9
STEREOISOMERSCANBEFURTHER
SUBDIVIDED...
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Stereoisomers:Enantiomers
CHEM212/211 OrganicBites3 Chapter5 10
ISOMERS differentcompoundswiththesamemolecularformulaSTRUCTURAL differentconnectivity
STEREOISOMERS sameconnectivity,differentorientationinspace
ENANTIOMERS
non
superimposable
mirror
image
stereoisomersDIASTEREOMERS nonmirrorimagestereoisomers
ENANTIOMERS
caraway mint
O
H
O
H
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Stereoisomers:Diastereomers
CHEM212/211 OrganicBites3 Chapter5 11
ISOMERS differentcompoundswiththesamemolecularformulaSTRUCTURAL differentconnectivity
STEREOISOMERS sameconnectivity,differentorientationinspace
ENANTIOMERS
non
superimposable
mirror
image
stereoisomersDIASTEREOMERS nonmirrorimagestereoisomers
DIASTEREOMERS
trans2,3dichloro2hexene cis2,3dichloro2hexene
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CHEM212/211 OrganicBites3 Chapter5 12
HOWDOESCHIRALITYFITINTOTHIS
PICTURE?
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CHEM212/211 OrganicBites3 Chapter5 13
MORE3DVISUALIZATIONS...
Section3 Stereochemistry
Chapter
5
Chiral
MoleculesStructuralIsomersvs.Stereoisomers
EnantiomersandChirality
OpticalRotationandRacemicMixtures
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Chirality
CHEM212/211 OrganicBites3 Chapter5 14
CHIRALOBJECT onewithanonsuperimposablemirrorimage1.ENANTIOMERSARE(BYDEFINITION)APAIROFCHIRALOBJECTS
2.CHIRALOBJECTSARESAIDTOHAVECHIRALITY
ENANTIOMERS
caraway mint
O
H
O
H
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Chirality
CHEM212/211 OrganicBites3 Chapter5 15
CHIRALOBJECT onewithanonsuperimposablemirrorimage1.ENANTIOMERSARE(BYDEFINITION)APAIROFCHIRALOBJECTS
2.CHIRALOBJECTSARESAIDTOHAVECHIRALITY
ENANTIOMERS
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Chirality
CHEM212/211 OrganicBites3 Chapter5 16
ENANTIOMERS
CHIRALOBJECT onewithanonsuperimposablemirrorimage1.ENANTIOMERSARE(BYDEFINITION)APAIROFCHIRALOBJECTS
2.CHIRALOBJECTSARESAIDTOHAVECHIRALITY
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Chirality
CHEM212/211 OrganicBites3 Chapter5 17
ENANTIOMERS
CHIRALOBJECT onewithanonsuperimposablemirrorimage1.ENANTIOMERSARE(BYDEFINITION)APAIROFCHIRALOBJECTS
2.CHIRALOBJECTSARESAIDTOHAVECHIRALITY
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CHEM212/211 OrganicBites3 Chapter5 18
WEARECHIRALOBJECTS!
ANDSOAREMOSTMOLECULESOFLIFE...
WHICHAREALSOMOSTLYONLY
ONEENANTIOMER!
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BiologicalChirality
CHEM212/211 OrganicBites3 Chapter5 19
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BiologicalChirality
CHEM212/211 OrganicBites3 Chapter5 20
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BiologicalChirality
CHEM212/211 OrganicBites3 Chapter5 21
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BiologicalChirality
CHEM212/211 OrganicBites3 Chapter5 22
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BiologicalChirality
CHEM212/211 OrganicBites3 Chapter5 23
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CHEM212/211 OrganicBites3 Chapter5 24
ENANTIOMERS
HAVE
THE
SAMEPHYSICALPROPERTIES...
(IDENTICALINTERMOLECULARFORCES)
...EXCEPT
FOR
OPTICAL
ROTATION!
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OpticalRotation
CHEM212/211 OrganicBites3 Chapter5 25
BoilingPoint 99.5C 99.5C
Meltingpoint 115C 115C
Density 0.808 0.808
SpecificRotation[] +13.5 13.5
(opticalrotation) opticallyactive opticallyactive
(+)2butanol ()2butanol
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CHEM212/211 OrganicBites3 Chapter5 26
WHATISOPTICALROTATION?
...ANDHOWDOWEMEASUREIT?
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CHEM212/211 OrganicBites3 Chapter5 27
MORE3DVISUALIZATIONS...
Section3 Stereochemistry
Chapter5 ChiralMolecules
StructuralIsomersvs.Stereoisomers
EnantiomersandChirality
OpticalRotationandRacemicMixtures
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MeasuringOpticalRotation
CHEM212/211 OrganicBites3 Chapter5 28
OPTICALROTATION rotationofplanepolarizedlightasit
passesthroughachiralobject1. ALLCHIRALMOLECULESWILLROTATEPLANEPOLARIZEDLIGHT
2. ENANTIOMERSROTATEINEQUALAMOUNTS,OPPOSITEDIRECTIONS
POLARIZEDLIGHT
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MeasuringOpticalRotation
CHEM212/211 OrganicBites3 Chapter5 29
OPTICALROTATION rotationofplanepolarizedlightasit
passesthroughachiralmolecule1. ALLCHIRALMOLECULESWILLROTATEPLANEPOLARIZEDLIGHT
2. ENANTIOMERS
ROTATE
IN
EQUAL
AMOUNTS,
OPPOSITE
DIRECTIONS
POLARIMETER
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CHEM212/211 OrganicBites3 Chapter5 30
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CHEM212/211 OrganicBites3 Chapter5 31
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CHEM212/211 OrganicBites3 Chapter5 32
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CHEM212/211 OrganicBites3 Chapter5 33
MeasuringOpticalRotation
POLARIMETER
OPTICALROTATION rotationofplanepolarizedlightasit
passesthroughachiralmolecule1. ALLCHIRALMOLECULESWILLROTATEPLANEPOLARIZEDLIGHT
2. ENANTIOMERS
ROTATE
IN
EQUAL
AMOUNTS,
OPPOSITE
DIRECTIONS
...BUTWECANNOTPREDICTWHICHDIRECTIONANENANTIOMERWILL
ROTATELIGHTBASEDONSTRUCTURE!
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OpticalRotationData
CHEM212/211 OrganicBites3 Chapter5 34
(+)2butanol ()2butanol
SpecificRotation[] = observedrotationangle
(concentration)(celllength)
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OpticalRotationData
CHEM212/211 OrganicBites3 Chapter5 35
SpecificRotation[] +13.5 13.5opticallyactive opticallyactive
clockwise counterclockwise
(+)2butanol ()2butanol
dextrorotatory levorotatory
(+)rotation ()rotation
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OpticalRotationData
CHEM212/211 OrganicBites3 Chapter5 36
SpecificRotation[] +31.4 31.4opticallyactive opticallyactive
clockwise counterclockwise
(+)glutamicacid ()glutamicacid
dextrorotatory levorotatory
(+)rotation(natural)
()rotation(unnatural)
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RacemicMixtures
CHEM212/211 OrganicBites3 Chapter5 37
SpecificRotation[] 0
notopticallyactive!
racemicmixture
1:1mixture
RACEMICMIXTURES 50:50mixturesof(+)and()
(+)2butanol ()2butanol
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RacemicMixtures
CHEM212/211 OrganicBites3 Chapter5 38
1:1mixture (+)2butanol&()2butanol
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CHEM212/211 OrganicBites3 Chapter5 39
COMPOUNDSTHATROTATEPLANE
POLARIZEDLIGHT(i.e.CHIRALOBJECTS)
ARESAIDTOBEOPTICALLYACTIVE...
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TheFirstOpticallyActiveObjects
CHEM212/211 OrganicBites3 Chapter5 40
THEFIRSTENANTIOMERS!
LOUIS
PASTEUR
(1822
1895)
()tartaricacid (+)tartaricacid
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TheFirstOpticallyActiveObjects
CHEM212/211 OrganicBites3 Chapter5 41
TARTARICACID opticalrotationclockwise
LOUISPASTEUR(1822 1895)
()tartaricacid (+)tartaricacid
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TheFirstOpticallyActiveObjects
CHEM212/211 OrganicBites3 Chapter5 42
RACEMICACID nomeasuredopticalrotation
LOUISPASTEUR(1822 1895)
()tartaricacid (+)tartaricacid
50:50
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OrganicBites3:MainObjectives
CHEM212/211 OrganicBites3 Chapter5 43
1. Identifystructuralisomersvs.stereoisomers.
2. Define/identifyenantiomersanddiastereomers.
3. Recognize/Identifychiralobjects.
4. Understandopticalrotationand(+)/()notation.5. Explainthetermsopticallyactiveandracemic
mixture.