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7/27/2019 HoaLapThe VN

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HHA LA LP THP TH

StereochemistryStereochemistry


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Chirality Handedness: gng tay phi khng

chng kht vi gng tay tri. i tng nh qua gng khc vi itng gc ban u.

=>


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Chiral Carbons Carbon t din vi 4 nhm th khc

nhau l chiral. nh qua gng ca n s l hp cht

khc nhau (enantiomer). =>


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Mt phng i xng gng

Nu hai nhm gingnhau, carbon lachiral.

Phn t c mt phngi xng th khng lchiral.*

Lu ! Nu khng c mt phng i xng,phn tc th l chiral hoc achiral. nh quagng c chng kht ln nhau hay khng.


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H

Cl

H

Cl Are these twostructures identical?

mirror


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HCl

HCl


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enantiomersenantiomers

Cc ng phn lp

th

mnh quagng khng chng

kht ln nhau l

enantiomers.enantiomers.


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Stereoisomers ng phn hnh hc: cis-trans isomers.

Enantiomers: nonsuperimposable mirror images,different molecules.=>

cis-1,2-dichlorocyclopentane trans -1,2-dichlorocyclopentane

H

Cl

H

Cl

H

Cl

H

Cl

H

Cl

Cl

H

H

Cl

Cl

H


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diasteriomersdiasteriomers

CH3

CH3

H

H

cis

trans

ng phn lp th m

khng phi l nh quagng ca nhau ldiastereomers.diastereomers.

H

CH3

H

CH3

H

CH3

H

CH3


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Diastereomers

Stereoisomers that are not mirror images. Geometric isomers (cis-trans)

Cc phn t c hai hoc nhiu chiral carbons.


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Alkenes

Cis-trans isomers are not mirror images,so these are diastereomers.

C C

H H

CH3H3C

cis-2-butenetrans-2-butene

C C

H

H3C

CH3

H =>


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Properties of Diastereomers Diastereomers c tnh cht vt l khc

nhau: m.p., b.p. Tch d dng.

Enantiomers khc trong phn ng vicc phn t chiral khc v lm quaymt phng nh sng phn cc.

Enantiomers kh tch khi nhau.


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MMt phn tt phn t ll chiralchiralnnu 2u 2 nh qua gng cnh qua gng caa

chchng khng chng khng chng khng kht ln nhau.t ln nhau.

A molecule isA molecule is achiralachiralif its two mirror image formsif its two mirror image forms

areare chchng khng kht (superposable).t (superposable).

ChiralityChirality


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BrBrClCl

HH

FF

Bromochlorofluoromethane is chiralBromochlorofluoromethane is chiral

It cannot beIt cannot besuperposed pointsuperposed point

for point on itsfor point on itsmirror image.mirror image.


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BrBrClCl

HH

FF


HH

ClClBrBr

FF

cho thcho thy khng chy khng chngngkhkht, quay phn tt, quay phn t 180180quanh trquanh trc c ng.ng.


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BrBrClCl

HH

FF


HH

ClClBrBr

FF


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Another lookAnother look


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are enantiomers with respect to each otherare enantiomers with respect to each other

vv

nh qua gng khng chnh qua gng khng chng khng khttll enantiomersenantiomers

EnantiomersEnantiomers


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IsomersIsomers

ConstitutionalConstitutionalIsomersIsomers

StereoisomersStereoisomers

EnantiomersEnantiomers DiastereomersDiastereomers

Stereoisomersthat are not

mirror images.

Stereoisomers thatare nonidentical

mirror images


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ChlorodifluoromethaneChlorodifluoromethaneis achiralis achiral


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ChlorodifluoromethaneChlorodifluoromethaneis achiralis achiral

hai chai cu tru trc lc lnh qua gngnh qua gng,,nhng khng lnhng khng lenantiomers,enantiomers,bbi vi v chchngng

chchng khng khttc ln nhau.c ln nhau.


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Trung tm lTrung tm lp thp th

The Stereogenic CenterThe Stereogenic Center


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Nguyn tNguyn t carboncarboncc bbn nhn nhm thm th khkhc nhauc nhau

ccng ng c gc gi:i:chiral centerchiral centerasymmetric centerasymmetric centerstereocenterstereocenter

The Stereogenic CenterThe Stereogenic Center

ww

xx yy

zz

CC


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A molecule with a single stereogenicA molecule with a single stereogenic

center is chiral.center is chiral.

BromoBromochlorochlorofluorofluoromethanemethane is an example.is an example.

Chirality and stereogenic centersChirality and stereogenic centers

ClCl FF

BrBr

HH

CC


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A molecule with a single stereogenicA molecule with a single stereogenic

center is chiral.center is chiral.

22--Butanol is another example.Butanol is another example.

Chirality and stereogenic centersChirality and stereogenic centers

CHCH33

OHOH

HH

CC CHCH22CHCH33


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Examples of molecules with 1 stereogenic centerExamples of molecules with 1 stereogenic center

CHCH33

CC

CHCH22CHCH33

CHCH22CHCH22CHCH22CHCH33CHCH33CHCH22CHCH22

a chiral alkanea chiral alkane


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Linalool, a naturally occurring chiral alcoholLinalool, a naturally occurring chiral alcohol

OHOH


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1,21,2--Epoxypropane: a stereogenic centerEpoxypropane: a stereogenic center

can be part of a ringcan be part of a ring

OO

HH22CC CHCHCHCH33

attached to the stereogenic center are:attached to the stereogenic center are:

HH

CHCH33OCHOCH22

CHCH22OO


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Limonene: a stereogenicLimonene: a stereogenic

center can be part of acenter can be part of aringring

CHCH33

HH CC

CHCH33

CHCH22

attached to theattached to thestereogenic center are:stereogenic center are:

HH

CHCH22CHCH22CHCH22CH=CH=

C=C=


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MMt phn tt phn t chchcc 1 stereogenic center1 stereogenic center

phphi li l chiral.chiral.

nhngnhng, m, mt phn tt phn t cc 2 ho2 hoc nhic nhiuu

stereogenic centers cstereogenic centers c thth ll chiralchiralhohoc khngc khng


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i xi xng trong nhng trong nhng cng cu tru trc achiralc achiral

Symmetry in AchiralSymmetry in AchiralStructuresStructures


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Symmetry tests forSymmetry tests forachiralachiral structuresstructures

Phn tPhn t cc mmt pht phng ng i xi xng hong hoc trung tm c trung tm i xi xngngll achiralachiral..


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A plane of symmetry bisects a molecule into twoA plane of symmetry bisects a molecule into twomirror image halves. Chlorodifluoromethanemirror image halves. Chlorodifluoromethane

has a plane of symmetry.has a plane of symmetry.

Plane of symmetryPlane of symmetry


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A plane of symmetry bisects a molecule into twoA plane of symmetry bisects a molecule into twomirror image halves. Chlorodifluoromethanemirror image halves. Chlorodifluoromethane

has a plane of symmetry.has a plane of symmetry.



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A molecule with a plane of symmetrycannot be chiral Example

2-Chloropropane (a) has a plane of symmetry but 2-chlorobutane (b) does not


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A plane of symmetry bisects a molecule into twoA plane of symmetry bisects a molecule into twomirror image halves.mirror image halves.11--BromoBromo--11--chlorochloro--22--fluoroethene has a planefluoroethene has a plane

of symmetry.of symmetry.



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A plane of symmetry bisects a molecule into twoA plane of symmetry bisects a molecule into twomirror image halves.mirror image halves.11--BromoBromo--11--chlorochloro--22--fluoroethene has a planefluoroethene has a plane

of symmetry.of symmetry.



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A point in the center of theA point in the center of themolecule is a center ofmolecule is a center ofsymmetry if a line drawnsymmetry if a line drawnfrom it to some element,from it to some element,when extended an equalwhen extended an equal

distance in the oppositedistance in the oppositedirection, encounters andirection, encounters an

identical element.identical element.

Center of symmetryCenter of symmetry


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Locating a Stereocenter (ChiralCarbon)

CH3 CH C

OH

OH

O

Lactic acid

*


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CH3 CH2 CH2 CH2 CH2 C CH2 CH2 CH2 CH3

Br

H

*

Locating a Stereocenter


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O

CH3

H*


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H CH3no stereocenter


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Carvone: mirror-image isomershave different flavors and odors!

O

CH3

C

CH3

CH2

*

Enantiomers. Many of the properties of


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y p penantiomers are identical.

ClH

HClsolubility in water

boiling point

melting point

Enantiomers. However, if enantiomers are


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,different compounds they must have adifferent names and different properties.

ClH

HClRotation of the plane ofpolarized light (opticalrotation).

Taste and smell

biological activity(R)-2-chlorobutane

(S)-2-chlorobutane


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Enantiomers have differentb iolog ical act iv i ty .

Enantiomers have different properties

H

O

H

O

(-)-carvone

oil of spearmint(+)-carvone

oil of caraway


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H

O

H

O

(-)-carvone

oil of spearmint(+)-carvone

oil of caraway


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The Biological Importance of Chirality The binding specificity of a chiral receptor sitefor a chiral molecule is usually only favorable inone way


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"How would you like tolive in Looking-GlassHouse, Kitty? I wonder ifthey'd give you milk inthere? Perhaps Looking-glass milk isn't good to

drink...".

Through the Looking Glass by

Lewis Carroll

Alice looked through the keyhole of this door into the Looking Glass garden (the Cathedral garden)

Is looking glass


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Is looking glass

milk safe to drink?

?

Different enantiomers of a drug


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ff m f g

can have different effects.

amphetamineH2NNH2H H

stimulant adversecardiovasculareffects

Problem: Are A and B identical or enantiomers?


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Manipulate B to see if it will become superposable with A

Exchange 2 groups to try to convert B into A One exchange of groups leads to the enantiomer of B

Two exchanges of groups leads back to B


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The Cahn Ingold PrelogThe Cahn Ingold Prelog

RR--SS Notational SystemNotational System

Assign (R) or (S)


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g ( ) ( )

Assign a priority number to each group attached tothe chiral carbon.

Atom with highest atomic number assigned the

highest priority #1 Working in 3D, rotate molecule so that lowestpriority group is in back.

Draw an arrow from highest to lowest priority group. Clockwise = (R), Counterclockwise = (S)

If the order of decreasing precedence traces aIf the order of decreasing precedence traces aclockwise path the absolute configuration isclockwise path the absolute configuration is RR If theIf the


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ab

c

d

a b

c

d

Order of decreasing rank:Order of decreasing rank:

aa >> bb > c >> c > ddclockwiseclockwise

RRanticlockwiseanticlockwise

SS

clockwise path, the absolute configuration isclockwise path, the absolute configuration is RR. If the. If the

path is anticlockwise, the configuration ispath is anticlockwise, the configuration is SS..


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((SS))--22--ButanolButanol

CC OHOH

HH33CC

HHCHCH33CHCH22

Enantiomers of 2Enantiomers of 2--butanolbutanol

CCHOHO

CHCH33

HH CHCH22CHCH33

((RR))--22--ButanolButanol


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The CahnThe Cahn--IngoldIngold--Prelog RulesPrelog Rules


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Orient the molecule so that lowest-ranked (lightest)substituent points away from you. Trace the path fromhighest to lowest. Clockwise (R), Counter Clockwise (S)

E ti f 2E ti f 2 b t lb t l


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((SS))--22--ButanolButanol

CC OHOH

HH33CC

HHCHCH33CHCH22

Enantiomers of 2Enantiomers of 2--butanolbutanol

CCHOHO

CHCH33

HH CHCH22CHCH33

((RR))--22--ButanolButanol

St i t i iSt i t i i


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HHHH33CC

HH

HH

Stereogenic center in a ringStereogenic center in a ring

R or S ?R or S ?

RR

CHCH22C=C >C=C > CHCH22CHCH22 >> CHCH33 >> HH

Groups with double or triple bonds are assignedi iti if th i t d li t d


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priorities as if their atoms were duplicated ortriplicated

Vinyl vs isopropylVinyl vs isopropyl



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Name them using R- S- designation

(R)(R)

--11

--bromobromo

--1chloroethane1chloroethane

http://www.cem.msu.edu/~reusch/VirtualText/sterism3.hthttp://www.cem.msu.edu/~reusch/VirtualText/sterism3.ht

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