ORD

Optical Rotatory Dispersion

1. O PTICAL R OTATORY D ISPERSION By- Manish Sahu M.Sc. Chemistry (Final) Sp.- Physical Chemistry

2. SYNOPSIS OPTICAL ROTATORY DISPERSION HISTORY FUNDAMENTALS OF ORD COTTON EFFECT TYPES OF ORD CURVES APPLICATIONS OF CD

3. OPTICAL ROTATORY DISPERSION :- The specific rotation ( α ) changes with wavelength is called optical rotatory dispersion (ORD). The rate of change of specific rotation with wavelength is called optical rotatory dispersion(ORD) it is used for structural determination of carbonyl compound.

4. HISTORY Optical rotation caused by compound changed with wavelenght of light was first noted by “ Biot ” in 1817.

5. FUNDAMENTALS OF ORD Plane polarized light Optical activity and optical active compound Specific rotation Circular birefringence Circular dichroism

6. PLANE POLARIZED LIGHT A polarized light vibrating in a single plane perpendicular to the direction of propagation is called plane polarised light.

7. OPTICAL ACTIVITY Certain organic compound when placed in a path of a plain polarized light, it rotates the plain polarized light through a certain angle. This property of the compound to rotate plane polarized light is called optical activity. For a compound to be optically active, it must be chiral in nature(asymmetric character).

8. SPECIFIC ROTATION A 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 decimetre and a sample concentration of 1 gram per millilitre. [ α ] = where, α = angle of rotation in degrees l = path length is in decimetre d = density of liquid is in g 100/ml α l × d

9. INSTRUMENTATION FOR ORD

10. CIRCULAR BIREFRINGENCE The difference in indices of refraction for right circularly polarized light (RCPL) & left circularly polarized light (LCPL) is known as circular birefringence.

11. CIRCULAR DICHROISM Some materials posses special properties of absorption of the left circularly polarised light to different extend the right circularly polarised light. This phenomenon is called as circular 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.

12. COTTON EFFECT 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.

13. TYPES OF ORD CURVES They are of two types 1) plain curves 2) cotton effect curve (a) single cotton effect curves (b) multiple cotton effect curves

14. PLAIN CURVES The curves obtained do not contain any peak and that curve do not cross the zero rotation line. E.g. Compounds exhibiting such plane curves are alcohols and hydrocarbons

15. SINGLE COTTON EFFECT CURVES This curve will show maximum and minimum curve at maximum absorption from longer wavelength to words the cotton effect region. Cotton effect said to be positive cotton effect where the peak is at a higher wavelength then trough.

16. MULTIPLE COTTON EFFECT CURVES In this types of curves two or more peaks and trough are obtained. E.g. Functional group camphor etc exhibits such curves.

17. APPLICATIONS OF CIRCULAR DICHROISM SPECTROSCOPY Protein secondary structure determination. pH, heat or solvent induced structural change could be detected by CD. Structure aspects of nucleic acid, polysaccharides, harmones etc.

18. REFERENCES 1. Instrumental method of chemical analysis, 5 th edition page no:- 2,468- 2,481 by :- G.R. Chatwal & S.K. Anand 2. Spectroscopy of organic compounds, New age international limited, sixth edition, page no:- 611-627 by :- P.S. Kalsi 3. Instrumental method of chemical analysis, 26 th edition :- M-286 to M-307 by :- B.K. Sharma 4. Organic spectroscopy principles and applications, Narosa publishing house:-482 – 496 by :- Jag Mohan