Optical rotatory dispersion

1. Presented by,
Sujit R. Patel,
Dept. Of Pharmaceutics,
M.M.C.P. ,Belgaum.

2.  Fundamentals Of ORD.
 Optical Rotatory Dispersion.
 Cotton Effect.
 The ORD Curve.
 Circular Dichroism.
 Octant Rule.
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3. • ORD refers to the change in optical rotation with
the change in wavelength of light source. i.e. applied
only in optically active compounds.
• Optical rotation caused by compound changed with
wavelength of light was first noted by Biot in 1817.
• ORD curves in recent years are made use in
structural determination by comparing the curve
obtain from compound believed to have related
structures particularly applied to carbonyl
compounds.
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4. Natural light is having two components electric
component and magnetic component, and both are
perpendicular to each other in different planes.
Both these electric component and magnetic
components are also perpendicular to the direction of
propagation of light.
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5. UNPOLARISED LIGHT
NATURAL LIGHT
POLARISED LIGHT
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6. I. Linear or plane polarized light.
II. Circular polarized light.
III. Elliptically polarized light.
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8. A polarized light vibrating in a single plane
perpendicular to the direction of propagation
is called plane polarised light.
 A light wave is characterized by an electric
field vector Ē and a magnetic field vector Ĥ
which are perpendicular to each other and in
phase. The two vectors are also perpendicular
to the direction of propogation.
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9.  When vibration of light are along a circle lying in
a plane perpendicular to the direction of
propagation the light is called circular polarized
light.
 Represent a wave in which the electrical
component & the magnetic component spirals
around the direction of propagation (vibration) of
the ray, either clockwise (or right handed or
dextrorotatory.) OR counterclockwise (or left
handed or levorotary).
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10.  Linearly polarized light can be regarded as the resultant
of two equal and opposite beams of circularly polarized
light i.e.., as a combination of left and right circularly
polarized light.
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12.  When vibration are along a ellipse lying in a plane
perpendicular to the direction of propagation the light is called
elliptically polarized light
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14.  The difference in indices of refraction for right
circularly polarized light (RCPL) & left circularly
polarized light (LCPL) is know as circular
birefringence.
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15.  The specific rotation of a chemical compound
[α] is defined as the observed angle of optical
rotation α when plane-polarized light is passed
through a sample with a path length of 1
decimeter and a sample concentration of 1 gram
per 1 millilitre
 where,
α – Angle of Rotation in degrees
l –path length is in decimeters
d – density of liquid is in g 100 ⁄ ml 1
T–Temperature.
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16. A negative value means levorotatory rotation and a
A negative value means levorotatory rotation and a
positive value means dextrorotatory rotation.
positive value means dextrorotatory rotation.
 Some examples:
 Some examples:
Sucrose +66.47°
Sucrose +66.47°
cholesterol −31.5°
cholesterol −31.5°
Camphor +44.26°
Camphor +44.26°
Penicilin V +223
Penicilin V +223
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17. FARADAY EFFECT :-
FARADAY EFFECT :-
Any liquid or solution, when placed in a
Any liquid or solution, when placed in a
magnetic field ,, rotates the plane of polarized light
magnetic field rotates the plane of polarized light
because of the effect of magnetic field upon the motion of
because of the effect of magnetic field upon the motion of
electrons in the molecule.
electrons in the molecule.
INDEX OF REFRACTION (η) :-
INDEX OF REFRACTION (η) :-
The ratio of velocity of ray of light in
The ratio of velocity of ray of light in
vacuum (c) to its velocity in medium (v) i.e. η= C/V
vacuum (c) to its velocity in medium (v) i.e. η= C/V
Small differences in the refractive indices for right & left
Small differences in the refractive indices for right & left
circularly polarized light cause an appreciable rotation of
circularly polarized light cause an appreciable rotation of
the plane polarized light.
the plane polarized light.
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18. Optical activity :-
Optical activity :-
Ability to rotate plane of polarized light ..
Ability to rotate plane of polarized light
Optically active compound :-
Optically active compound :-
Certain organic compound when placed in a path of
Certain organic compound when placed in a path of
a plain polarized light, it rotates the plain polarized light
a plain polarized light, it rotates the plain polarized light
through a certain angle. This property of the compound
through a certain angle. This property of the compound
to rotate plane polarized light is called optical activity.
to rotate plane polarized light is called optical activity.
For a compound to be optically active, it must be chiral
For a compound to be optically active, it must be chiral
in nature(Asymmetric character).
in nature(Asymmetric character).
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19. Optical
Optical activity is not seen in symmetrical molecules
activity is not seen in symmetrical molecules
due to equal rotation in opposite directions getting
due to equal rotation in opposite directions getting
cancelled. The isomer that rotates the plane of
cancelled. The isomer that rotates the plane of
polarization to the left is called levo isomer (-) and to the
polarization to the left is called levo isomer (-) and to the
right is called dextro isomer (+).
right is called dextro isomer (+).
To be optically active ,, a molecule must not possessed
To be optically active a molecule must not possessed
any one of following symmetry elements ::
any one of following symmetry elements
1) Centre of symmetry
1) Centre of symmetry
2) Plane of symmetry
2) Plane of symmetry
3) An Proper axis
3) An Proper axis
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20.  The specific rotation [α] changes with
wavelength is called optical rotatory
dispersion (ORD) .
OR
 The rate of change of specific rotation with
wavelength is called Optical rotatory
dispersion (ORD) .
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21.  The rate of change of specific rotation with
wavelength is known as optical rotary dispersion .
 Drude has shown that the specific rotation may be
expressed as a function of wavelength by an equation,
[α] = k1 + k2 + k3 +-----
λ2 – λ12 λ2 – λ22 λ2 – λ23
 where
 λ- Wavelength of measurement
 k1,k2 ,k3 – constants that can be identified with the
wavelength of maximum absorption of optically active
absorption bands.
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22. 22
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23. Specific
Rotation
α
Wavelength λ
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24.  From graph,
 From graph,
A-Represents the plain positive ORD curve ::
A-Represents the plain positive ORD curve
The specific Rotation
The specific Rotation
increases with decreasing wavelength.
increases with decreasing wavelength.
B – Represents the plain negative ORD curve ::
B – Represents the plain negative ORD curve
Plain – implies that there exist no maximum or minima
Plain – implies that there exist no maximum or minima
in the curve.
in the curve.
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25.  The combination of circular birefringence and circular
dichroism in which the optically active bands are observed ,
such phenomenon called as cotton effect.
 Optically active bands are absorption bands of the
chromophores which are either intrinsically asymmetric or
which becomes asymmetric because of the interaction with
asymmetric environment.
 E.g.. 1) Hexahelicene molecule which itself act as
chromophore.
 2) Carbonyl group which is symmetric but becomes optically
active in an asymmetric environment.
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26.  They are of two types
 They are of two types

 1) Plain curves
1) Plain curves

 2) Anamolous curves
2) Anamolous curves
a) Single cotton effect curves
a) Single cotton effect curves
b) Multiple cotton effect curves
b) Multiple cotton effect curves
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27.  The curves obtained do not contain any peak and
that curve do not cross the zero rotation line
 Such waves are obtained for compounds which
do not have absorption in the wavelength region
where optical activity is being examined
 E.g..compounds exhibiting such plane curves are
alcohols and hydrocarbons
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28. 28
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29.  These curve on the other hand shows a
number of extreme peaks and troughs
depending on the number of absorbing groups
and therefore known as anomolous dispersion
of optical rotation.
 This type of curve is obtained for
compounds ,which contain an asymmetric
carbon atom and also contains chromophore.
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30.  These are anomolous dispersion curves which
shows maximum and minimum both of them
occurring in the region of maximum absorption.
 If an approaching the region of cotton effect from
the long wavelength ,one passes first through
maximum (peak) and then a minimum (trough)
,the cotton effect said to be positive . (Positive
Cotton effect is where the peak is at a higher
wavelength than the trough).
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32. Ifthe trough is reached first and the peak it is called a
negative cotton effect curves.
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33. The
The vertical distance between ‘peak’ and ‘trough’ is
vertical distance between ‘peak’ and ‘trough’ is
called amplitude ‘a’ and is convently expressed in
called amplitude ‘a’ and is convently expressed in
hundreds of degrees.
hundreds of degrees.
Molecular amplitude, a =ǿ22 -- ǿ11
Molecular amplitude, a =ǿ ǿ
100
100
Where,
Where,

 ǿ22 – molar rotation of extreme peak or trough from
ǿ – molar rotation of extreme peak or trough from
large wavelength.
large wavelength.

 ǿ11 -- molar rotation of extreme peak or trough from
ǿ molar rotation of extreme peak or trough from
shorter wavelength.
shorter wavelength.
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34.  Inthis type of curves two or more peaks and
trough are obtained .
 E.g.
functional group i.e. Ketosteriods ,
Camphor etc exhibits such curves .
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35. 35
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36. Some materials posses special properties of absorption of the left
circulary polarised light to different extent than the right circularly
polarised light.This phenomenon is called as circularly dichroism.
The electric field of a light beam causes a linear displacement of
charge when interacting with a molecule, whereas the magnetic field of it
causes a circulation of charge.
These two motions combined result in a helical displacement when
light impinges on a molecule (both field vectors in the same place are of
the same direction but at different moments of time).
The magnitude of circular dichroism is expressed by the ellipticiy.
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37. CIRCULAR DICHROISMː –
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38. An ordinary spectrophotometer can be adapted
to measure circular dichroism. It is only
necessary to provide some means of production
r and l circularly polarized radiation.
For this purpose a plane polarized beam can be
passed through a quartz-wave plate. If the plate
is rotated from -45o to +45o , first r and l
circularly polarized light is produced
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40. APPLICATIONS OF CIRCULAR DICHROISM (CD) SPECTROSCOPY
APPLICATIONS OF CIRCULAR DICHROISM (CD) SPECTROSCOPY
PROTEIN CONFORMATION:-
PROTEIN CONFORMATION:-
The CD spectrum of aaprotein can provide aainformation about the relative amounts of
The CD spectrum of protein can provide information about the relative amounts of
the major types of secondary structure within the protein in solution.
the major types of secondary structure within the protein in solution.
CD spectra of the α-helix β conformation and the random coil of poly-L-amino acids
CD spectra of the α-helix β conformation and the random coil of poly-L-amino acids
are distinctly different form each other.
are distinctly different form each other.
NUCLEIC ACID CONFORMATION:-
NUCLEIC ACID CONFORMATION:-
The CD spectrum of aasingle stranded nucleic acid may be calculated fairly accurately
The CD spectrum of single stranded nucleic acid may be calculated fairly accurately
form aaknowledge of its nearest neighbor frequency. Thus any differences between the
form knowledge of its nearest neighbor frequency. Thus any differences between the
calculated and measured CD spectrum must be due to variation in structure, such as
calculated and measured CD spectrum must be due to variation in structure, such as
double-strandness.
double-strandness.
The CD spectra are frequently used to study changes in the structure of nucleic acids
The CD spectra are frequently used to study changes in the structure of nucleic acids
such as: the los of helicity of single stranded nucleic acids as aafunction of temperature
such as: the los of helicity of single stranded nucleic acids as function of temperature
or pH structural changes on binding cation and proteins.
or pH structural changes on binding cation and proteins.
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41. DIFFERENECES BETWEEN ORD AND CD
DIFFERENECES BETWEEN ORD AND CD
OPTICAL ROTATORY DISPERSION CIRCUALR DICHROISM
(ORD) (CD)
ORD is If the refractive indices of the Circular dichroism is the differential
sample for the left and right handed absorption of left and right handed
polarized light are different, when the circularly polarized light
components are recombined , the plane
polarized radiation will be rotated through
and angle α
ORD spectra are dispersive CD spectra are absorptive
In ORD the circular polarized light is used In CD the circular polarized lgiht is used
is not converted to elliptical light and is converted to elliptical light
ORD graphs are obtained by plotting CD graphs are obtained by ploting molar
specific rotation vs wavelength ellipticity vs wavelength.
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42. The octant rule was first formulated by Moffitt
et al for correlation of the sign of the cotton
effect of chiral cylohexanone derivatives with
their absolute configration.
The space around carbonyl group is divided
into eight sector about x,y,z axis.
This rule only applies to substituted
cyclohexanone
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43. It states that atoms lying on the back upper left and back
It states that atoms lying on the back upper left and back
lower right, then octant make positive contribution.
lower right, then octant make positive contribution.
(Positive rotation).
(Positive rotation).
If groups on back upper right and back lower left then
If groups on back upper right and back lower left then
the octants make negative contribution. (Negative
the octants make negative contribution. (Negative
rotation).
rotation).
Substituents lying in the co-ordinate planes make no
Substituents lying in the co-ordinate planes make no
contribution to the rotatory dispersion.
contribution to the rotatory dispersion.
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44. Axial and equatorial group Axial and equatorial group
Positivie cotton effect negativie cotton effect
Axial and equatorial group Axial and equatorial group positive
negative cotton effect cotton effect
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46.  If an optically active chromophore takes part in a
reaction the extent of the reaction can sometimes be
followed by observing the reduction of the cotton effect.
Eg:- if hydrochloric acid is added to a solution of (+) 3-
methylcyclehexanone in methanol, the cotton effect gets
reduced by 93% because of dimethy ketal formation.In
alcohol only 33% reduction and in isopropyl alcohol
there occurs no reduction.
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47. Determination
Determination of position of keto group and the
of position of keto group and the
confrigration of ring system in a sterodial ketone of
confrigration of ring system in a sterodial ketone of
unknown constitution.
unknown constitution.
Study of conformational changes:
Study of conformational changes:
when molecule exist in more than one confirmation in
when molecule exist in more than one confirmation in
solution, each conformer will have its own ORD or CD
solution, each conformer will have its own ORD or CD
curve and the sign and magnitude of the cotton effect
curve and the sign and magnitude of the cotton effect
will change with the change of conformer population,
will change with the change of conformer population,
caused either by a change of solvent polarity or by a
caused either by a change of solvent polarity or by a
change in temperature
change in temperature
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48. A. Chetwal GR & Anand SK, Instrumental method
of chemical analysis, 5TH edition page no:- 2.468-
2.481.
B. Kalsi PS, Spectroscopy Of Organic Compounds,
New age international limited, sixth edition:611-
627.
C. Jag Mohan, Organic Spectroscopy Principles
And Applications, Narosa publishing hose:482-
496.
D. Sharma BK, Instrumental method of chemical analysis,
26TH edition:-M-286 to M-307.
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49. 1. What is meant by ORD ? Discuss the principle and
application of ORD .(Nov 98).
2. What is optical rotatory dispersion & how is it useful
in characterization of substances.(Jul 98).
3. ORD & Circular Dicroism.(2000).
4. Cotton effect .(2004).
5. Note on the principle & application of ORD &
Circular Dicroism .(2004,Oct 08).
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50. 6. Write an account on fundamental principles of ORD.
(2005).
7. Explain Circular Dicroism.(2006).
8. Describe the instrumentation used for measuring
circular dichroism.(Oct 09).
9. Explain the phenomena of optical rotation & circular
polarization. Giving a schematic diagram, write
about an ORD instrument. What are the applications
of ORD & CD.(May 10 & 12).
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