Optical rotatory dispersion and circular dichroism presentation

Detailed description for optical rotatory description and circular dichroism to understand it properly in a better way.

1. OPTICAL ROTATORY DISPERSION AND CIRCULAR DICHROISM Chaitrali jadhav . Roll no:- 07.

2. SOME IMPORTANT BASICS TO BE REMEMBERED IN ORD: LIGHT : It is an electromagnetic radiation consists of both vibrating electric and magnetic vectors perpendicular to each other & having the wavelength of 4000-7700 angstroms . Study of light is called Optics . WAVE LENGTH : The distance between successive crests or peaks of a wave. It is denoted by “ λ ”. CHROMOPHORE : An atom or group whose presence is responsible for the colour of a compound.

3. OPTICAL ROTATORY DISPERSION (ORD) DEFINITION : Rate of change of specific rotation with change in wave length is called as ORD . It is used for structural determination of carbonyl compounds . FUNDAMENTAL PRINCIPLES OF ORD : Plane polarized light . Optical activity Specific rotation . Circular Birefrengence . Optical Rotation.

4. PLANE POLARIZED 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.

5. OPTICAL ACTIVITY  The compounds which are having the ability to rotate the plane of polarised light are called optically active compounds . This property of compound is called optical activity. It is measured by Polarimeter . Compound which rotates plane of polarised light to right ( clock wise) is called DEXTROROTATORY & is denoted by ( + ) sign.

6.  If the compound rotates plane of polarised light towards left side (anti clock wise) is called LEVOROTATORY & is denoted by ( - ) sign . Image of Polarimeter :

7.  When a ray of monochromatic polarized light strikes a solution, several phenomenon’s occurs like – 1. Reflection on the surface . 2. Refraction . 3. Rotation of plane polarization 4 . Absorption.

8. 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 . IT DEPENDES ON VARIOUS FACTORS LIKE : Nature of substance . Length of the column . Conc. of the sol . Temp of the sol . Nature of the solvent . Wavelength of the light used.

9. CIRCULAR BIREFRINGENCE  If two equal & opposite beams of CPL & PPL passes through an optically active compound it result in characteristic phenomenon is called Circular Birefringence.

10. OPTICAL ROTATION When a plane polarized light(PPL)t is passed through optically active compound due to it’s Circular Birefrigence results in unequal rate of propagation of left & right circularly polarized rays . This unequal rate of propagation of both left & right circularly polarized light deviates the PPL from it’s original direction & it is called as OPTICAL ROTATION . Optical rotation caused by compound changed with wavelength of light was first noted by Biot in 1817.

11. CIRCULAR DICHROISM  Circular Dichroism occurs when the two circularly polarized components of PPL are absorbed differentially. When the component emerges out there is an imbalance in their strength & the resultant two will not be linearly polarized but elliptically polarized & this phenomenon is called as CIRCULAR DICHROISM

12. COTTON CURVES  French physicist discovered it & he described it as, The combination of circular dichroism and circular birefringence is known as cotton effect . Djerassi & Klyne suggested that rotatory dispersion curves should be classified in to two main types: 1. Plain curves. 2. Cotton effect curves/ anomalous curves.

13. PLAIN CURVES ANOMALOUS CURVES These curves will show the high peaks & troughs which depends on the absorbing groups. So they are called as Anomalous dispersion of optical rotation . These curves will obtain for the compounds which are having asymmetric carbon & chromophore which absorbs near UV region . These are again divided into 2 types, they are : 1 . Single cotton effect curves 2. Multiple cotton effect curves. These are normal or plain curves. These curves occurs at absorption maximum . The curves obtained do not contain any peak or inflections and that the curve do not cross the zero rotation line . These curves obtained for compounds which don’t have any absorption in wavelength where optically active compounds are examined . Ex: Hydrocarbons, Alcohols etc.

14. INSTRUMENTATION ORD Light source Monochromator Polarizer Analyzer Sample tube photomultiplier CD Light source Polarizer Sample tube Photomultiplier Recorder

15. CD SPECTROSCOPE

16. DIFFERENCE B/W ord & cD ORD CD PLANE POLARIZED LIGHT DISPERSIVE PHENOMENA PLANE POLARIZED IS USED & IS NOT CONVERTED TO ELLIPTICAL LIGHT GRAPHS ARE OBTAINED BY SPECIFIC ROTATION V/S WAVELENGTH CIRCULARLY POLARIZED LUGHT ABSORPTIVE PHENOMENA CIRCULAR POLARIZED LIGHT IS USED & IS CONVERTED TO ELLIPICITY GRAPHS ARE OBTAINED MOLAR ELLIPICITY V/S WAVE LENGTH

17. ADVANTAGES Simple and quick experiments No extensive preparation Relatively low concentrations/amounts of sample Microsecond time resolution Any size of macromolecule Better resolution Better sensitivity Easier to assign

18. APPLICATIONS CD/ORD of protein. Qualitative analysis of molecules. Enzyme co-factor evaluation. CD/ORD of proteins. CD as finger printing. CD/ORD of nucleic acids. CD of B-DNA is different as compared to A-DNA. Evidence for base stacking.

19. REFERENCES WWW. Science direct.com WWW.notes.com Principles & techniques by Avinash Upadhyay WWW.scribd.com