chem 212 - chirality % optical rotation review

7/24/2019 CHEM 212 - Chirality % Optical Rotation Review

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IntroductoryOrganicChemistry

Chem 212&Chem 211

Dr.LauraPavelkaDepartmentofChemistry

Pulp&Paper104

[email protected]

ORGANICBITES3:CHIRALITY&OPTICALROTATION


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CHEM212/211 OrganicBites3 Chapter5 3

MAKESUREYOUKEEPALLYOURISOMERS

STRAIGHT!


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StructuralIsomers


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


ISOMERS differentcompoundswiththesamemolecularformulaSTRUCTURAL differentconnectivity


STEREOISOMERS

trans2,3dichloro2hexene cis2,3dichloro2hexene


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Stereoisomers




STEREOISOMERS

trans1,3dichlorocyclohexane cis1,3dichlorocyclohexane


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Conformers


CONFORMERS rotationalisomers



*CONFORMERSARENOTTRUEISOMERS ONLYDIFFERENT

REPRESENTATIONSOFTHESAMECOMPOUND*


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ResonanceStructures


RESONANCESTRUCTURES 2+Lewisstructurestorepresentthesamemolecule



*RESONANCESTRUCTURESARENOTISOMERS ONLY

DIFFERENTREPRESENTATIONSOFTHESAMECOMPOUND*


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STEREOISOMERSCANBEFURTHER

SUBDIVIDED...


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Stereoisomers:Enantiomers




ENANTIOMERS

non

superimposable

mirror

image

stereoisomersDIASTEREOMERS nonmirrorimagestereoisomers

ENANTIOMERS

caraway mint

O

H

O

H


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Stereoisomers:Diastereomers




ENANTIOMERS

non

superimposable

mirror

image

stereoisomersDIASTEREOMERS nonmirrorimagestereoisomers

DIASTEREOMERS

trans2,3dichloro2hexene cis2,3dichloro2hexene


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HOWDOESCHIRALITYFITINTOTHIS

PICTURE?


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MORE3DVISUALIZATIONS...

Section3 Stereochemistry

Chapter

5

Chiral

MoleculesStructuralIsomersvs.Stereoisomers

EnantiomersandChirality

OpticalRotationandRacemicMixtures


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Chirality


CHIRALOBJECT onewithanonsuperimposablemirrorimage1.ENANTIOMERSARE(BYDEFINITION)APAIROFCHIRALOBJECTS

2.CHIRALOBJECTSARESAIDTOHAVECHIRALITY

ENANTIOMERS

caraway mint

O

H

O

H


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Chirality




ENANTIOMERS


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Chirality


ENANTIOMERS




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Chirality


ENANTIOMERS




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WEARECHIRALOBJECTS!

ANDSOAREMOSTMOLECULESOFLIFE...

WHICHAREALSOMOSTLYONLY

ONEENANTIOMER!


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BiologicalChirality



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BiologicalChirality



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BiologicalChirality



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BiologicalChirality



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BiologicalChirality



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ENANTIOMERS

HAVE

THE

SAMEPHYSICALPROPERTIES...

(IDENTICALINTERMOLECULARFORCES)

...EXCEPT

FOR

OPTICAL

ROTATION!


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OpticalRotation


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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WHATISOPTICALROTATION?

...ANDHOWDOWEMEASUREIT?


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MORE3DVISUALIZATIONS...

Section3 Stereochemistry

Chapter5 ChiralMolecules

StructuralIsomersvs.Stereoisomers

EnantiomersandChirality

OpticalRotationandRacemicMixtures


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MeasuringOpticalRotation


OPTICALROTATION rotationofplanepolarizedlightasit

passesthroughachiralobject1. ALLCHIRALMOLECULESWILLROTATEPLANEPOLARIZEDLIGHT

2. ENANTIOMERSROTATEINEQUALAMOUNTS,OPPOSITEDIRECTIONS

POLARIZEDLIGHT


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passesthroughachiralmolecule1. ALLCHIRALMOLECULESWILLROTATEPLANEPOLARIZEDLIGHT

2. ENANTIOMERS

ROTATE

IN

EQUAL

AMOUNTS,

OPPOSITE

DIRECTIONS

POLARIMETER


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POLARIMETER


passesthroughachiralmolecule1. ALLCHIRALMOLECULESWILLROTATEPLANEPOLARIZEDLIGHT

2. ENANTIOMERS

ROTATE

IN

EQUAL

AMOUNTS,

OPPOSITE

DIRECTIONS

...BUTWECANNOTPREDICTWHICHDIRECTIONANENANTIOMERWILL

ROTATELIGHTBASEDONSTRUCTURE!


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OpticalRotationData



SpecificRotation[] = observedrotationangle

(concentration)(celllength)


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OpticalRotationData


SpecificRotation[] +13.5 13.5opticallyactive opticallyactive

clockwise counterclockwise


dextrorotatory levorotatory

(+)rotation ()rotation


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OpticalRotationData


SpecificRotation[] +31.4 31.4opticallyactive opticallyactive

clockwise counterclockwise

(+)glutamicacid ()glutamicacid

dextrorotatory levorotatory

(+)rotation(natural)

()rotation(unnatural)


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RacemicMixtures


SpecificRotation[] 0

notopticallyactive!

racemicmixture

1:1mixture

RACEMICMIXTURES 50:50mixturesof(+)and()



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RacemicMixtures


1:1mixture (+)2butanol&()2butanol


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COMPOUNDSTHATROTATEPLANE

POLARIZEDLIGHT(i.e.CHIRALOBJECTS)

ARESAIDTOBEOPTICALLYACTIVE...


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TheFirstOpticallyActiveObjects


THEFIRSTENANTIOMERS!

LOUIS

PASTEUR

(1822

1895)

()tartaricacid (+)tartaricacid


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TARTARICACID opticalrotationclockwise

LOUISPASTEUR(1822 1895)



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RACEMICACID nomeasuredopticalrotation

LOUISPASTEUR(1822 1895)


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OrganicBites3:MainObjectives


1. Identifystructuralisomersvs.stereoisomers.

2. Define/identifyenantiomersanddiastereomers.

3. Recognize/Identifychiralobjects.

4. Understandopticalrotationand(+)/()notation.5. Explainthetermsopticallyactiveandracemic

mixture.

chem 212 - chirality % optical rotation review

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