It is an analytical method used for measuring the polarization and optical activity of various molecules.

1. POLARIMETRY
Presented by- Anjali Sharma

2. MODERN POLARIMETER CLASSICAL POLARIMETER

3. POLARIMETRY
It is the study of the rotation of polarised light by transparent optically active
substance.
Polarimetry is based upon the existence of optical activity in a substance.
This is a type of qualitative and quantitative analytical technique.
Polarimeter is a scientific instrument which measures change in rotation of
plane polarised light.
Optical activity is unique character for a molecule.

4. OPTICAL ACTIVITY
It is the ability of a chiral molecule to rotate the plane of plane polarised light.
As per pasteur absence of symmetry is the necessary criterion for optical activity.
The two arrangements that have asymmetric molecule cannot be superimposed.
A chiral molecule is non superimposable on its mirror image & have carbon atom
attached to four different group also known as chiral center.

5. CONFIGURATION : The representation which shows the sapatial
arrangement of the groups of atoms constituting a stereoisomers is known as
its confiugration.
EPIMERS are the optical isomers that differ only in the configuration around
one asymmetric carbon atom (having more than one asymmetric carbon).

6. Enantiomers are chiral molecules that are mirror images of one another & are
non- superimposable in nature.
Diastereomers are stereoisomers that are not mirror images of one another &
are non- superimposable in nature.

7. PLANE POLARISED LIGHT
Plane polarised light oscillates only in a single plane when normal light oscillating in
all direction passes through a polarizer such as nicol prism.
Normal light consists of electromagnetic waves that oscillates in all direction.
Circularly polarised light represents a wave represents a wave in which the electrical
component spirals around direction of propagation of the ray,either clockwise or
anticlockwise.

9.  Electric field of plane polarised light is composed of two components.
I. Right circularly polarised (RCP)
II. Left circularly polarised (LCP)
The plane beam is vector sum of these two component.
The extent of retarding the plane polarised light through a medium is known as
refractive index of that medium.

10. When the medium is optically inactive both the component s are retarded to the
same extent.
when the medium is optically active the component is retarded to different extent
due to difference in refractive indices of the medium for LCP & RCP.
This phenomenon of the difference in the velocity of LCP& RCP light is called
circular birefringence.
Due to circular birefringence plane of polarization inclined at an angle.
 Polarization involves the separation of natural light into its mutually perpendicular
components.

11. The angle of incidence selected is such that the criticle angle of reflection is
exceeded for one ray but not for the other.
But the beam emerging out is not parallel to the incident beam and this can be
overcomed by cementing the seconed prism.
It also reduces the loss of intensity.
Linearly polarised light is passed through the optically active solution & the plane
polarised light rotated by an angle.

12. SPECIFIC ROTATION
Change in the orientation of monochromatic plane –polarized light, per unit
distance –concentration product , as the light passes through a sample of a
compound in solution.
It is a property of a chiral chemical compound.
It is an intensive property.
Used in quantitative analysis of optically active solute using polarimetry.

13. POLARIMETER
Principle :Polarimeter measures the rotation of polarised lights as it passes
through an optically active fluid.
The measured rotation can be used to calculate the value of solution
concentrations.
Construction : A polarimeter consists of a polarized light source,an analyzer,a
graduated circle to measure the rotation angle and sample tube.
Working : The polarized light passes through the sample tube and exhibits angular
rotation to the left (-) or right (+).
On the side opposite the polarizer is the analyzer.
Visual fields are manually adjusted by the users to measure the optical rotation
angle by using optics.

15. TYPES OF POLARIMETER
Laurent’s half-shade polarimeter
Biquartz polarimeter
Lippich polarimeter
X-ray polarimeter
Quartz-wedge polarimeter

16. APPLICATIONS
Quantitative application-
For determining the specific rotation if concentration is known.
For determining the concentration if specific rotation is known.
Differentiating optical substances from optically inactive species.
Qualitative application-
ORD & CD measurements can be used for studying configuration and
confirmation in UV region.
For distinguish between D & L isomeric forms.
For identification & determination of purity of substance.