1.INTRODUCTION 2.THEORY AND PRINCIPLE 3.OPTICAL ROTATORY DISPERSION 4.CIRCULAR DICHROISM 5.APPLICATION

1. BY:
N.SHABANA PARVEEN
III-PHARMD

2. CONTENTS
 INTRODUCTION
 THEORY AND PRINCIPLE
 OPTICAL ROTATORY DISPERSION
 CIRCULAR DICHROISM
 APPLICATION

4. INTRODUCTION:
 Polarimetry is a sensitive, nondestructive technique
for measuring the optical activity exhibited by
inorganic and organic compounds.
 A compound is considered to be optically active if
linearly polarized light is rotated when passing
through it.
 The amount of optical rotation is determined by the
molecular structure and concentration of chiral
molecules in the substance.

5.  The term Polarimetry may be referred as the
study of the rotation of polarised light by
transparent optically active substance.
 This is a type of qualitative and quantitative
analytical technique as both identification
and estimation of the compound can be done

6. PLANE POLARISED LIGHT
 According to wave theory of light, an ordinary ray light
is considered to be vibrating in all planes at right angle
to the direction of propagation. If this ordinary ray of
light is passed through a Nicol prism, the emergent ray
has its vibration only in one plane. This light having
wave motion in only one plane is known as Plane
Polarised Light.

7. Vertical plane Horizontal plane
The vibration may all be restricted to one direction only,in
the perpendicular plane  plane polarised light.
Unpolarised light gets converted into a plane polarised light
by simply passing it through a lens called a NICOL prism.

8.  A plane polarized light which consists of two components of
fixed magnitude rotating in opposite directions to one another;
 The right circulatory polarized light
 The left circulatory polarized light
 Plane polarized light is the vector sum of these two
components

9. PRINCIPLE:
OPTICALACTIVITY:
 When certain organic liquids,solutions(sugar) or
quartz crystal are placed in the path of polarised
light,the plane of polarisation is rotated.
 The property by virtue of which the plane of
polarisation is rotated is known as optical activity
and the substane with this property is called optically
active substance.

10.  Substances which rotate the plane of polarised light
to right side (clockwise) are called dextro rotatory(+)
while which rotate towards left (anticlockwise) are
called levo rotatory(-).
 A mixture of these two varieties in equal proportions
will be optically inactive and is called racemic form.
 Example:lactic acid.

11. The magnitude of rotation depend upon the
following factors:
 Nature of Substance
 Length of liquid column ( l ) through which light
passes.
 Concentration of the solution.
 Nature of the solvent.
 Temperature of the solution (t)
 Wavelength of the light used

12. SPECIFIC ROTATION:
The Rotatory Power of a given solution is
generally expressed as specific rotation. It is the number
of degree of rotation of plane polarized light produced by
one gram of the substance per ml. The measurements is
carried out at temp using sodium light. The Specific
rotation can be Calculated by the following relation:
 [α] = specific rotation, T = temperature,
 λ = wavelength, θ= optical rotation,
 c = concentration in g/100ml, l = optical path length in dm.

13. THEORY OF OPTICALACTIVITY:
 Structures of optically active compounds have
asymmetric structures.
 A structure is said to be asymmetric if it is not
superimposable on its mirror image.
 Example:human hand.

15.  In case of organic compounds,asymmetry is a
consequence of tetrahedral geometry of sp3 carbon
atom
 Presence of asymmetric carbon atom leads to
asymmetry in the molecule and compound shows
optical activity.Presence of asymmetric structure in
organic compound is the basis of optical activity.

16. OPTICAL ROTATORY DISPERSION:
 The rate of change of specific rotation with
wavelength is known as optical rotatory dispersion.
 Optical rotatory dispersion is a technique related to
optical activity.
FUNDAMENTAL PRINCIPLES OF ORD:
 Plane polarized light.
 Optical activity
 Specific rotation.
 Circular Birefrengence.
 Optical Rotation.

17. PLANE POLARISED LIGHT:
 Light from ordinary lamp consists of waves vibrating in
many different planes.
 When it is passed through polaroid lense it is found to
vibrate in one plane is said to be plane polarised light
or polarised light.

18. OPTICALACTIVITY:
 The compounds which are having the ability to rotate
the plane of polarized light are called optical active
compound.
 This property of compounds is called optical activity.
 Measured by Polarimeter
 Dextrorotatory
 Levorotatory

19. SPECIFIC ROTATION:
 It is defined as the rotation produced by a solution of length
10cm & unit concentration (1gm/ml) for given wavelength
of light at the given temperature.It is denoted by α.
 The specific rotation changes with wavelength.
 The specific rotation may expressed as a function of
wavelength by an equation,
 [α ]=k1/(λ2-λ1
2 )+k2/(λ2-λ2
2 )+k3/(λ2-λ3
2)+……
 Where λ is wavelength of measurements & k1,k2,k3…are
constants that are identified with the wavelength of
maximum absorption of optically active absorption bands.

20. CIRCULAR BIREFRINGENCE:
 The difference in indices of refraction for right
circularly polarized light (RCPL) & left circularly
polarized light (LCPL) is know as circular
birefringence.
 As a result of circular birefringence the beam emerges
from medium still plane polarised but with plane of
polarisation inclined at an angle θ to the incident beam.

21. ORD CURVES:
 A=plane positive ORD curve(i.e,the specific rotation
increases with decreasing wavelength).
 B=plane negative ORD curve “plain” implies that
there exist no maximum or minimum in the curve.

22. CIRCULAR DICHORISM:
 In addition to the different speeds EL and ER it is also
possible that these 2 components get absorbed to
different extents.
 If this happens the magnitude of EL would be no longer
equal to that of ER, and E will no longer oscillate along
a single line.In fact,E will trace out an ellipse.
 The medium is said to exhibit circular dichorism(CD)
and the transmitted light would become elliptically
polarised.

24.  In absorption spectroscopy the reduced intensity I gets
related to the intensity of the incident radiation I0 by the
following equation,
I= I0e-kl
 Where l denotes the distance travelled in the medium
and k is absorption coefficient.The angle of elliptically
ψ is given as follows:
ψ= π/ λ(kL-kR)
 Where kL and kR refer to the adsorption coefiicients for
EL and ER which is analogous to [α ]= α x 100/l x c.

25. ψ = ψ/lc
Where l denotes the path length in centimeter and the
molecular elliptically per unit length [θ] is
[θ] = [ψ]M/100
It is given in terms of extinction coefficients for EL and
ER as,
[θ]=3.3 x 102(EL-ER).

26. COTTON EFFECT:
 The combination of circular birefringence and circular
dichroism in which the optically active bands are
observed ,such phenomenon called as cotton effect.
 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

27.  They are of two types
1) Plain curves
2) Anamolous curves
a.) Single cotton effect curves
b.) Multiple cotton effect curves

28. PLAIN CURVES:
 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.

29. ANAMOLOUS CURVES:
 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.

30. SINGLE COTTON EFFECT RULES:
 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).

32.  If the trough is reached first and the peak it is called a
negative cotton effect curves.

33.  The vertical distance between ‘peak’ and ‘trough’ is
called amplitude ‘a’ and is convently expressed in
hundreds of degrees.
 Molecular amplitude, a =ǿ2 - ǿ1/100
Where,
 ǿ2 – molar rotation of extreme peak or trough from
large wavelength.
 ǿ1 - molar rotation of extreme peak or trough from
shorter wavelength

34. MULTIPLE COTTON EFFECT RULES:
 In this type of curves two or more peaks and trough
are obtained .
 E.g. functional group i.e. Ketosteriods ,Camphor etc
exhibits such curves.

36. DIFFERENCE BETWEEN ORD & CD:

37. APPLICATION:
 Polarimetric method is a simple and accurate means for
determination of structure in micro analysis of
expensive and non-duplicable samples.
 It is employed in quality control, process control and
research in the pharmaceutical, chemical,essential oil,
flavor and food industries.
 It is so well established that the United States
Pharmacopoeia and the Food & Drug Administration
include polarimetric specifications for numerous
substances.

38. Research Applications:
 Research applications for polarimetry are found in
industry, research institutes and universities as a means
of:
 Isolating and identifying unknowns, crystallized from
various solvents or separated by HPLC.
 Evaluating and characterizing optically active
compounds by measuring their specific rotation and
comparing this value with the theoretical values found
in literature.

39.  Investigating kinetic reactions by measuring optical
rotation as a function of time.
 Monitoring changes in concentration of an optically
active component in a reaction mixture,as in enzymatic
cleavage.
 Analyzing molecular structure by plotting optical
rotatory dispersion (ORD) curves over a wide range of
wavelengths.
 Distinguishing between optical isomers.

40. Pharmaceutical Applications:
 Determines product purity by measuring specific
rotation and optical rotation of: Amino acids, Amino
sugars, Analgesics, Antibiotics,Cocaine, Dextrose
Diuretics Serums,Steroids Tranquilizers Vitamins.
 Utilizes polarimetry for incoming raw materials
inspection of: Camphors,Citric acid, Glyceric acid
Gums,Lavender oil, Lemon oil,Orange oil,Spearmint
oil.

41.  Ensures product quality by measuring the
concentration and purity of the following
compounds in sugar based foods, cereals and syrups:
Carbohydrates,Fructose,Glucose,Lactose,Levulose,M
altose,Raffinose,Sucrose,Various Starches Natural
monosaccharides
 Analyzes optical rotation as a means of identifying
and characterizing:Natural polymers,
Biopolymers,Synthetic polymers.