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Ord and cd ppt
- 1. CD & ORD SPECTROSCOPY BOBBY SOLANKI M.Sc. Chemistry Sharda University Greater Noida
- 2. OPTICAL ROTATORY DISPERSION ▪ It can be define as the rate of change of specific rotation with change in wavelength. ▪ Measuring optical rotation as a function of wavelength is termed optical rotatory dispersion (ORD) spectroscopy. ▪ It can be measured by polarimeter.
- 3. FUNDAMENTALS OF ORD ▪ Plane polarized light. ▪ Optical activity. ▪ Specific rotation. ▪ Circular Birefringence. ▪ Optical Rotation.
- 4. PLANE POLARISED LIGHT ▪ Light from ordinary lamp consists of waves vibrating in many different planes. ▪ When it is passed through polaroid's lens, it is found to vibrate in one plane and is said to be plane polarized light.
- 5. OPTICAL ACTIVITY ▪ The compounds which are having the ability to rotate the plane of polarized light are called optical active compounds. ▪ This property of compound is called optical activity. ▪ It is measured by polarimeter. ▪ Compound which rotates of polarized light to right (clock wise) is called DEXTROROTATORY & is denoted by (+) sign.
- 6. ▪ If the compound rotates plane of polarized light towards left side (anti clock wise) is called LEVOROTATORY & is denoted by (-) sign. ▪ Enantiomers are optically active compounds.
- 7. For a compound to be optically active it must be devoid of the following properties 1. Plane of symmetry 2. Center of symmetry 3. Alternating – axis of symmetry
- 8. SPECIFIC ROTATION ▪ It is defined as the rotation produced by a solution of length 10cm and unit concentration for given wavelength of light at the given temperature. ▪ It is denoted by (a).
- 9. CIRCULAR BIREFRINGENCE ▪ If two equal & opposite beams of CPL & PPL passes through an optically active compound it result in characteristic phenomenon called circular birefringence.
- 10. OPTICAL ROTATION ▪ When a plane polarized light (PPL) is passed through optically active compound due to its circular birefringence 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 its original direction & it is called as OPTICAL ROTATION.
- 11. CIRCULAR DICHROISM • Some materials posses special properties of absorption of the left circular polarized light to different extent than the right circularly polarized light.
- 12. • 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.
- 13. Cotton curves ▪ The combination of these two effects in the region in which the optically active absorption bands are observed gives rise to the phenomenon called cotton effect and the curve arises.
- 14. There are two types of cotton curves. • 1. plane curve • 2. anomalous curve 1.Plane curve:- The curves obtained do not contain any peak and 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. Ex. hydrocarbons
- 15. 2. Anomalous curve: 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 anomalous dispersion of optical rotation.
- 16. ▪ This type of curve is obtained for compounds, which contain an asymmetric carbon atom and also contains chromophore. ▪ These are anomalous dispersion curves which shows maximum and minimum both of them occurring in the region of maximum absorption. ▪ approaching the region of cotton effect from the long wavelength, one passes first trough maximum(peak) and then a minimum (trough), the cotton effect said to be positive. Positive cotton effect is where the peak is at a
- 17. Higher wavelength than the trough. ▪ The opposite is called the negative cotton effect.