Binder Ord CD

7/25/2019 Binder Ord CD

1/13

The

relation

of

the

electric

field

vector

E

and the magnetic

field

vector

H

of

a

linearly

polarized

light

beam to

the direction

of

propagation

at a

given

time

is

shown

inFig.

12.2a.

The

two fields

oscillate

at right

angles

to

one

another

and

in

phase.

A

different

view

(Fig.

12.2b)

shows

only

the magnitude

and

direction

of the

electric

field

vector

as a function

of

time

I and

at

a

given

distance

z

-

z0

from

the

light

source.6

Both

relations

are

cosine functions

described

by Eq.

l2.l:

E

=

Eo

cos(2nn

-

2nz/)u)

-

Eo cos

a(t

-

z/

co)

(12.1)

where

z is

the

light

frequency,

=

co/

u

is

its

wavelength

(ca

is

the

speed

of light

in

vacuum),

Es

is

the

maximum

arnplitude

of

the

wave,

and,

a

=

2nu.

(b,

Figure

12.1.

(a)

Isotropic

and

(A)

anisotropic

(linearly

polarized)

light

beams

(ele6ric

field

only)

viewed

along

the

z

axis

toward

the

light

source.

[Adapted

with

permission

from

Solornons,

T. W.

G. Organic

Chemistry-

Copyright

@ 1978 John

Wiley

& Sons,

Inc., New York,

pp.244-245.1

Direclion

of

propogolion +

Time

+

Figure

12,2.

Linearly

polarized

light

(a,

at

a

given

time and

, at

a

given

place.)

[(a)

Reprinted

with

permissionfromBrcwster,

J.H.Topstereochem.

1961,2,1.

copyrighto

1967Johnwiley&Sons,

Inc.

and

()

adapted

with

permission

from

Snatzke,

G. Chem. IJnserer

Zeit.1981,

j5,

78.1

#

al

(bt

Direclion

of

propogolion +


2/13

(a)

right

circularly

polarized

light

light

propagation-

Source

k=0

+Z

observer

at

t=to

-+\

,rksr

^\'

I \

,w

alz-4

(b\

Figure

12'3'

Definition

of.ight

cpl.

(a)

A

=

ro.

the

electric

field

vector

describes

a right-handed

helix

as

viewed

toward

the

light

source

(z

increases

as

z

=

k(/12,

k

=

0,

r,2,

..

.

).

[Adapted

from

Harada,

N.

an


3/13

Figure

l2'5.

(a)

Right

cpl

ray

(only

electric

fields

are

shown)

from

one-quarter

wave

retardation

(see

also

Fig. 12.2).

(A)

The

instantaneous

electric

field

is

one-quarter

wavelengih

out

of

phase.

[Reprinred

with

permission

from

Brewster.

J.

H.

Top.

stereochem.

1967,2,

1.

copyright

o 1967

Jo-hn wiley

& Sons,

Inc.l

a

=

(nL-

n*)n//), ,

(in

rad)

(12.2)

s.=

(nL-

nR)1800//^,0

(in

deg)

(12.3)

Figure

12..

The

origin of

optical

activity.

Rotation

of linealry

polarized

light by superposition

of

left

(--)

and right

(-)

cpl.

Time-dependent

view

toward

the

light source

frorn

a

given poin1z

=;6

(left

to

right).

As

shown,

the

rotation

is

positive

(dextrorotation).

[Adapted

with

permission from Snatzke,

G.

Chem.

Unserer

tuit.

1981,

15,78.1

tll

6fri

@

lll

r

o


4/13

Figure

12.7.

Interaction

of

a

beam

of light

linearly

polarized

in

the ,r

direction

with

a chiral

molecule.

negolive

curve

Figure 12.8.

Optical rotatory dispersion

in transpalent

regions ofthe spectrum.

[Crabb,

P. In Snatzke, G.,

ed.,

Optical

Rotatory Dispersion

and Circular Dichrotsm

in Organic

Chemistry,

p.

2.

Copylight

O

1967

Heyden Son.

Adapted with

permission of

John

Wiley

Sons,

Ltd.l

OH

cf

+

0

Figure

12.9.

Dependence

ofAz

on wavelength.

Anomalous

dispersion.


5/13

UV:

mor

292

(=32)

ll

rlL->

4--(

'o

(+)

-

Comphor

200

300

400

Figure

12.10. Anomalous

ORD

curve of

(1R,4R)-(+)-camphor (-)

exhibiting

a

single

positive

CE.

Nomenclature of ORD curves;

the crossover

point

at

294

nm is an

optical

null,

[(D]

=

0.

The

isotropic

W:

spectrum of camphor

(--)

is superposed on

the

ORD

curve.

[Adapted

with

permission

from

Crabb,

P. ORD

and CD

in

Chemistry

and Biochemistry, Academic Press, Orlando,

FL,

1972,

p.

6]

l[O],1+ l[(D]rl

o=

1oo

(12.4)

uvl,,,o*

.^.4'*

- 1

,ff

-s

\.

UV

(o)

tol

x

lO-3

Figure 12.11,

(a)

Single

Cotton effect

ORD curve:

positive

CE with negative

rotation

in

the

visible

(UV

rna*

=

264

nm).

[Adapted

with

permission

from

Djerassi,

C. Proc.

Chem.

Soc.

Iondon

1964,

315.

Copyright O

Royal Society

of

Chemistry,

Science

Park,

Milton

Road, Cambridge

CB4

4WF,

UK.l.

(b)

Shape

of

an ORD

curve that

stems

from

superposition of

a positive CE

(-)

near

264 nm and

of

a

negative

(background)

CE

(-)

lying

at

shorter

wavelength.

[Adapted

with

permission

from

Snatzke,

G. Chem.

Unserer

Zeit. f981,

15, 78.1


6/13

(a)

+5.1

15

I

irl

2

I

r

(nm)

Figure

12.12.

(a)

UV

(electronic absorption'

EA) and

CD

(positive

CE)

spectra

of

(1R,4)-(+).canrphor.

1a.-aaptea

*itt,

permission

from

Crabb,

P.

ORD

and

CD

in

Chemistry

and

Biochensttt,

Academic

Press'

lunao,

pi1-,

iSlZ,p.

6.1.

(b)

cD

and

oRD

spectra

describing

the

posirive

cE

of

a^single

electronic

(isolate)transirion.

fAdaptedwithpermissionfromSnatzke,

G.Chem.

IlnsererZeit'

1981'

15,78'l

olo

o/o

olo

Figure

12.13.

Elliptically

polarized

light.

(a)

Equal

velocities

of transmission

give

n

o

rotationi

()

unequal

viocities

of

transmission

give

rotatiin,

(c)

unequal

velocities

and

unequal

absorptions

give

roation nd

ellipticalpolarization.[ReprintedwithpermissionfromLowry,T.M.opticalRotaoryPower,Dover,New

York,

1964,

p.

152.

where

the

symbols

c,

1,,

and

M

have

the

of

[cr,]

and

[]

(Section

1-3)'

in 10-1

deg

cm2

g-l

(t2.s)

(t2.6)

in

10

deg

cm2

mol-l

same

meanings

as

they

do

in

the

definitions

w=fi

rel=l#

Figure12.14. Ellipticallypolarizedlight(a)inaregionwherec=0'and(b)inaregionwherecr=positive

viewed

toward the

light

source.

Electric

field vectors

En >

Er- are

both

smaller than

Eo

(incident

cpl);

the

resultant vector

E

traces an

elliptical

path.

The

ellipticity

angle ry

is given

by

the

geometric construction:

arctangentofminoraxis/majoraxisa,wherea=En+ElandA=En-Er-.Sincebydefinition,Ae=eL

-

ep, ry is

positive if rr-

>

en.

lAdapted

from

Velluz, L,, Legrand.

M.,

and

Grosjean,M.

Optical

Circular

Dichroism,Y

erlrg

Chemie,

Weinheim,

1965,

pp.

22-23.1


7/13

Ia]

x

ro-,

[o]

x ro-'?

,",e6b

I

(nm)

'igure

12.15.

The

CD

and

ORD

curves

of a

simple hydroxyketone.

The

chirotopic chromophore

tesponsible

for

the

CE near 290

nm

is the

carbonyl

group

at

position

17a. The

shoulders

in

the

CD

band

are

due

to vibralional fine structure.

[Adapted

with

permission

from Crabb, P. and Parker,

A. C. In

Weissberger,

A.

and

Rossiter, B.

W.,

eds.,

Phy-scal

Methods

of

Chemstry, Part

IIIC,

Techniques

of

Chemistry,

Vol. 1, p.

209.

Copyright

O

1972

John

Wiley

&

Sons,

Inc.l


8/13

b.

Classifcation

of

Chromophores

The chromophores

that

are

analyzed by

means

of CD

measurements

naturally fall

into

two

broad

classes as

proposed

by

Moscowitz22

o

the

basis

of

symmetry

considerations

(Chapters

4

and 5)6'1e'33:

1.

Chromophores that

are

inherently achiral

by symmetry,

such

as

the

carbonyl

and

carboxyl

groups,

the

ordinary C:C double

bonds

(alkenes),

and

the

sulfoxide

moiety.

Each of

these,

when considered

without

substituents,

contains

at least one mirror

plane.

Chiral molecules

containing inherently

achiral

(symmetric)

chromophores exhibit

CEs

as

a

consequence of

chiral

perturbations arising

in

the

chromophore during

the

electronic excitation

of

the

latter.

These

perturbations

are

exerted

by substituents located in

the

vicinity

of

the

chromophore or

by

the molecular

skeleton

itself.

In

the

preceding

statement

we

have

purposely

used

the

language

that

one

finds

in most descriptions

of

such chromophores

in

the

literature. However,

as

has

already been

pointed

out, since all

points

in

a chiral molecule are

in

a

locally

chiral

environment,

the

notion of

an

inherently

achiral

moiety in a

chiral

molecule

is

fiction.

It

might

then

seem that the

proposed

bipartite

classification

of chromophores is invalid. In

fact,

the classification

has

an

experimental basis

(see

below); and it may also

be

retained

as a

matter

of

convenience.

2. Chromophores

that

are

inherently

chiral.

This

type of

chromophore

includes

compounds,

such

as

the

helicenes, in which

the

entire

molecule

acts

as

a single

chromophore.

Other

examples

are

disulfides,

biaryls,

enones,

cyclic

1,3-dienes

(e.g.,

Chapter

l1),

and strained

(twisted)

alkenes

(for

the latter, cf.

Section

9-

1.d). In

all of

these, the

chirality

is

built

into

the

chromophore. The

rotational

strengths

R

of

inherently chiral chromophores tend

to

be

very large

(see

Table

12.2).

TABLE

12.2.

Electronic

Transition Magnitudes'

g

Numbe/

cD

g=491x

lo,)

Ae t

Transition

Wavelength

l

(nm)

UV

o

JT

tl

__,-

\Cg,

3

-Methylcyclohexanone

JI

U

(-)-B-Pinene

(+)-Hexahelicene

(3, pg.

113)

oComparison

of

isotropic

(W)

and anisotropic

(CD)

electronic transition magnitudes

in

selected

chiral

molecules.

Adapted

with

permission

from

Mason. S.

F.

Molecular Optical Activity

and

the

Chiral

Discriminations, Cambridge

University

Press, Cambridge,

UK,

1982,

p.

49. T\e

data on

(+).se-hexahelicene

(in

CHCI3) is taken

from

Newman,

M.

S.,

Darlak,

R. S.,

and

Tsai,

L.

L

Am.

Chem.

Soc.

1967, 89,6t9t

with

Ae

=

tey3300.

The

dimensionless

ratio of

the

circular dichroic

to

isotropic

absorbance, previously called anisotropy or

dissymmetry

lactor.34

Theiransitins

for hexahelicene

are

both

presumed to be

of

the

r

-

n* typ .8l

30

0.8

2)

,I

298

185

16

1200

+0.48

+1.0

n-11

n-o-

(3s)

n*-

n

n^-fi;

E

-

TE*,

I

-

fi*

n-

n*

couplet

200

181

325

244

1.08

x

104

0.9

x

lOa

2.8

x l}a

4.8

x

104

-17.1

+17.0

+196

-216

7.0

7.1

NHu

NHz

7xlOa

6x104

-245

+

135

247

231

3l

2


9/13

\

o\^

-

n

\n

x

+CE

x

-CE

Figure

12,17.

Axial

haloketone

rule.

Br

+CE

1

l-cr-Br (equatorial):

+CE (as

in

rhe parent

ketone)

l1-p-Br

(axial):

{E

Figure12.18.

Applicationsoftheaxialhaloketonerule.(A)Positionofthehalogensubstituen.Thebromo

drivative

exhibited

a

negative

CE, hence

substitution

occurred

at

C(5).

(B)

determination

ofthe

absolute

Qonfiguration

of

the 1

1

-bromo

substituent

in

an 1

I

-bromo-

1 2-ketosteroid

(ref.

20,

p.

123).

,n-J. n

[ ^

d]

+CE

inCH3OH

+CE

+CE

Figure 12.19.

Conformational

rnobility in 2-chloro-5-methylcyclohexanones.

(A)

trans

isomer;

(B)

the

confonnational

equilibrium of

the

cis

isomer

is

shown

for

comparison;

(C)

dipole repulsion

in

the

trans

isomer.

9rHrr

o

(o)

Hrc

3

^

6) x c

vr\

GH'

-

U

-

\-\,-/

I

-

\_l_J-l

II

(a)Br

I

.

H

,r,

In A, the steroid

A ring

has beei:r

$)

8r

AB'

Figure

12.20.

Demonstration

of a boat

form

from chiroptical data.

inverted

for ease of

comparison

with Fig.

12.17.


10/13

(b)

Front

Seclors

Reor

Secrors

Figure 12.21.

Octant

rule

for

saturated ketones.

(a)

Signs of

the sctors

in a

left-handed

Cartesian

coordinate system;

()

projection

of

the

rear

(-z

hemisphere)

sectors.

[Adapted

with

permission

from

Snatzke, G.

Chem.

Unserer

Zeit.

1982,

16,

160.1

_[T ]_

Figure

12.22.

(a)

Stereoprojection

of

the cyclohexanone

ring

(chair

form)

in the

octant

diagram;

(D)

projecticn

of cyclohexanone

bonds.

View

facing

the carbonyl oxygen

with

signs

ofrear

octants.

[Reprinted

witir

permission

from

Snatzke.

G.

Angew.

Chem.

Int.

Etl.

EngI

1968,

7,

14.)

Figure

12.23. Octant

rule

projections

for

(+)-3-methylcyclohexanone

(rear

sectors).

(a)

Projection for

the

axial

conformer

(,S

configuration);

()

projection for

the

equatorial conformer

(R

configuration).

IReprinted

with

permission from Charney,

E. The

Molecular

Basis

of Optical Aclivity. Optical

Rotatory

Dsperson

ond

Circular

Dichroism,

p.

176.

Copyright

@

1979 John

Wiley

& Sons'

Inc.l

o

@

(b)

a)

o

(b)

a)

o


11/13

5

?

o

x

A

AhdFfu* '''

o'smoll

3

ohJtlfc H,r

,

o

o'+tzt

W___J

rlltr

.i;

olo

Figure

12.24. Semiquantitative

assessment

of

CE

magnitudes.

Octant

ule

projection

for

isorneric

l-,

2-,

and

3-cholestanones

(3-5,

respectively)

and

expermentally

observed

CE amplitudes

(see

Figs-

12.25

nd

12.26,

respecrively).

The

projection

outlined

with dashed

lines

is that

in

a

front

octant.

[Adapted

with

pennission frotn

Snatzke,

G.

Angew-

Clrcm.

Int. Ed.

Engl. 1968'

7' l4'l

\,nm

Figure12.25.

TheoRDspectraof5c,-cholestan-l-one3(-.-),-2-one4(-),and-3-one5(--)(methanol

solution).

[Adapted

from

Djerassi,

C.

optical

Rotatory

Dispersion,McGraw-Hill,

New

york,

1960,p.42.]

Figure

12.26. The

CD

spectra of

So-cholestan-l-one 3

(-

-)

and -3-one

5

(*)

(methanol

solution).

[Reprinted

with

permission

fiom

Djerassi,

C., Records,

R., Bunuenberg, E.,

Mislow, K.,

and

Moscowitz,

:A.

J.

Am.

Chern.

Soc.1962,84,4552.

Copyright

O

i962

Arnerican

Chemical

Society

l

;'

ol

b

X

X,n

m


12/13

rrndom coil

c-hclix

$forms

p-tums

Figure

12.44.

Organization

of

polypeptides

into

their

principal conformational

forms.

The

atoms \ilithin

the

rectangle

constitute

a

rigid

planar unit.

-fo

-40

+{

l{

I

N

t

I

x

6'

\

(nm)

Figure

12.46. Resolved

cD

spectrum

of the

pure

helical

form of

poly(r--alanin?,

jntl;

triiuoroethanol-trifluoroacetic

acid

(98.5:1.5

v/v).

The

bold

faced

curve

represents

the

experimental

data';r'.r'r

The

1go-nm

negative

CD

band

(--)

is

inferred

to facilitate

and

irnprove

the

curve

resolutioi.

t5"pd:""lrr.:

with

permissioi

from

euadrifoglio,

F.

and

Ur.y,

D.

-t't

. J.

Am.

Chem.

Soc.

1968, 90,2755.

Copyright

@'

1,

1968

American

Chemical

SocietY'l

930

o

6ao

o

o

{t

o

3ro

o

o

oto

I

o

;o

(b

-to

2@6

I

(nm)

(a)

220

t

(nm)

(b)

Figure 12.45.

(a)

CD

of

poly(r--glutamic acid)

(-)

and

poly(r--glutamate)

(-):

a

helix

(PGA'

pH

4.5) and

random coil

(PGA,

pH

8).

CD

of

N-acetyl-l-alanine-M-methylamide

(AAMA,----).

[Reproduced

with

permission

from

Johnson.

W. C., Jr.,

and Tinoco,

1.,

h.

J.

Am.

Chern.

Soc.1972,94,4389.

Copyright @

19?2

American

Chemical

Societyl.

()

CD of

poly(r-lysine):

(1)

cr

helix;

(2)

F

form:

(3)

random

coi.

[Reproduced

with

permission

from

Greenfield,

N. and Fasman,

G.

D. Biochemistry

1969,

8,

4108.

Copyright @

1969

American

Chemical

Society.l

POLY-L.ALANINE

Cr?i

I

toot

L

H.lh

I

roo

r,

t

l,oot

t nam Gt h

.li,\

\

Y


13/13

o

Ero

1J

30

ts

o

.?o

ot

0,

r

to

c)

I

o0

x

-

-10

230

)t,

nm

?30

)t,

nm

Figure

12.47. Comparison

of

CD

spectra of

three conformational

modes computed

(A)

from X-ray

diffraction

data and

CD

spectra

of lysozyme,.

myoglobin

and ribonucleases,

and

(B)

from CD spectra

of

the

pure conformational

forms of

poly(r--lysne)

(r

=

random

coil).

[Reproduced

with

permission from

Saxena.

V.

P. and

Wetlaufer.D.

B.

Proc.

Natl. Acad. Sci.

USA

l97t'

66' 969.1

b

.9

fll

(nm)

Figure

12.48.

The CD

spectra

of

adenylic

acid,

native

polyadenylic

acid

(poly

A),

and denatured

poly

A'

[Riprinted

with

permission

from

Freifelder,

D.

Physical

Biochemistry,

p.

467. Copyright

O 1976

W.

H.

Freeman

and ComPanY,

New

York.l

210

2tl

2eo

3{x,

Binder Ord CD

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