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Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
Optical rotatory dispersion
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Optical rotatory dispersion

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Optical rotatory dispersion

Optical rotatory dispersion

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  • 1. Presented by, Sujit R. Patel,Dept. Of Pharmaceutics, M.M.C.P. ,Belgaum.
  • 2.  Fundamentals Of ORD. Optical Rotatory Dispersion. Cotton Effect. The ORD Curve. Circular Dichroism. Octant Rule. 2 February 11, 2013 M.M.C.P.
  • 3. • ORD refers to the change in optical rotation with the change in wavelength of light source. i.e. applied only in optically active compounds.• Optical rotation caused by compound changed with wavelength of light was first noted by Biot in 1817.• ORD curves in recent years are made use in structural determination by comparing the curve obtain from compound believed to have related structures particularly applied to carbonyl compounds. 3 February 11, 2013 M.M.C.P.
  • 4. Natural light is having two components electriccomponent and magnetic component, and both areperpendicular to each other in different planes.Both these electric component and magneticcomponents are also perpendicular to the direction ofpropagation of light. February 11, 2013 M.M.C.P. 4
  • 5. UNPOLARISED LIGHT NATURAL LIGHT POLARISED LIGHT 5 February 11, 2013 M.M.C.P.
  • 6. I. Linear or plane polarized light.II. Circular polarized light.III. Elliptically polarized light. 6 February 11, 2013 M.M.C.P.
  • 7. 7February 11, 2013 M.M.C.P.
  • 8. A polarized light vibrating in a single plane perpendicular to the direction of propagation is called plane polarised light. A light wave is characterized by an electric field vector Ē and a magnetic field vector Ĥ which are perpendicular to each other and in phase. The two vectors are also perpendicular to the direction of propogation. 8 February 11, 2013 M.M.C.P.
  • 9.  When vibration of light are along a circle lying in a plane perpendicular to the direction of propagation the light is called circular polarized light. Represent a wave in which the electrical component & the magnetic component spirals around the direction of propagation (vibration) of the ray, either clockwise (or right handed or dextrorotatory.) OR counterclockwise (or left handed or levorotary). 9 February 11, 2013 M.M.C.P.
  • 10.  Linearly polarized light can be regarded as the resultant of two equal and opposite beams of circularly polarized light i.e.., as a combination of left and right circularly polarized light. 10 February 11, 2013 M.M.C.P.
  • 11. 11February 11, 2013 M.M.C.P.
  • 12.  When vibration are along a ellipse lying in a plane perpendicular to the direction of propagation the light is called elliptically polarized light 12 February 11, 2013 M.M.C.P.
  • 13. 13February 11, 2013 M.M.C.P.
  • 14.  The difference in indices of refraction for right circularly polarized light (RCPL) & left circularly polarized light (LCPL) is know as circular birefringence. 14 February 11, 2013 M.M.C.P.
  • 15.  The 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 decimeter and a sample concentration of 1 gram per 1 millilitre where, α – Angle of Rotation in degrees l –path length is in decimeters d – density of liquid is in g 100 ⁄ ml 1 T–Temperature. 15 February 11, 2013 M.M.C.P.
  • 16. A negative value means levorotatory rotation and aA negative value means levorotatory rotation and a positive value means dextrorotatory rotation. positive value means dextrorotatory rotation. Some examples: Some examples:Sucrose +66.47°Sucrose +66.47°cholesterol −31.5°cholesterol −31.5°Camphor +44.26°Camphor +44.26°Penicilin V +223Penicilin V +223 16 February 11, 2013 M.M.C.P.
  • 17. FARADAY EFFECT :-FARADAY EFFECT :- Any liquid or solution, when placed in a Any liquid or solution, when placed in a magnetic field ,, rotates the plane of polarized light magnetic field rotates the plane of polarized light because of the effect of magnetic field upon the motion of because of the effect of magnetic field upon the motion of electrons in the molecule. electrons in the molecule.INDEX OF REFRACTION (η) :-INDEX OF REFRACTION (η) :- The ratio of velocity of ray of light in The ratio of velocity of ray of light in vacuum (c) to its velocity in medium (v) i.e. η= C/V vacuum (c) to its velocity in medium (v) i.e. η= C/VSmall differences in the refractive indices for right & leftSmall differences in the refractive indices for right & left circularly polarized light cause an appreciable rotation of circularly polarized light cause an appreciable rotation of the plane polarized light. the plane polarized light. 17 February 11, 2013 M.M.C.P.
  • 18. Optical activity :-Optical activity :- Ability to rotate plane of polarized light .. Ability to rotate plane of polarized lightOptically active compound :-Optically active compound :- Certain organic compound when placed in a path of Certain organic compound when placed in a path of a plain polarized light, it rotates the plain polarized light a plain polarized light, it rotates the plain polarized light through a certain angle. This property of the compound through a certain angle. This property of the compound to rotate plane polarized light is called optical activity. to rotate plane polarized light is called optical activity. For a compound to be optically active, it must be chiral For a compound to be optically active, it must be chiral in nature(Asymmetric character). in nature(Asymmetric character). 18 February 11, 2013 M.M.C.P.
  • 19. OpticalOptical activity is not seen in symmetrical molecules activity is not seen in symmetrical molecules due to equal rotation in opposite directions getting due to equal rotation in opposite directions getting cancelled. The isomer that rotates the plane of cancelled. The isomer that rotates the plane of polarization to the left is called levo isomer (-) and to the polarization to the left is called levo isomer (-) and to the right is called dextro isomer (+). right is called dextro isomer (+).To be optically active ,, a molecule must not possessedTo be optically active a molecule must not possessed any one of following symmetry elements :: any one of following symmetry elements 1) Centre of symmetry 1) Centre of symmetry 2) Plane of symmetry 2) Plane of symmetry 3) An Proper axis 3) An Proper axis 19 February 11, 2013 M.M.C.P.
  • 20.  The specific rotation [α] changes with wavelength is called optical rotatory dispersion (ORD) . OR The rate of change of specific rotation with wavelength is called Optical rotatory dispersion (ORD) . 20 February 11, 2013 M.M.C.P.
  • 21.  The rate of change of specific rotation with wavelength is known as optical rotary dispersion . Drude has shown that the specific rotation may be expressed as a function of wavelength by an equation, [α] = k1 + k2 + k3 +----- λ2 – λ12 λ2 – λ22 λ2 – λ23 where λ- Wavelength of measurement k1,k2 ,k3 – constants that can be identified with the wavelength of maximum absorption of optically active absorption bands. 21 February 11, 2013 M.M.C.P.
  • 22. 22February 11, 2013 M.M.C.P.
  • 23. SpecificRotation α Wavelength λ 23 February 11, 2013 M.M.C.P.
  • 24.  From graph, From graph,A-Represents the plain positive ORD curve ::A-Represents the plain positive ORD curve The specific Rotation The specific Rotation increases with decreasing wavelength. increases with decreasing wavelength.B – Represents the plain negative ORD curve ::B – Represents the plain negative ORD curvePlain – implies that there exist no maximum or minimaPlain – implies that there exist no maximum or minima in the curve. in the curve. 24 February 11, 2013 M.M.C.P.
  • 25.  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. E.g.. 1) Hexahelicene molecule which itself act as chromophore. 2) Carbonyl group which is symmetric but becomes optically active in an asymmetric environment. 25 February 11, 2013 M.M.C.P.
  • 26.  They are of two types They are of two types 1) Plain curves 1) Plain curves 2) Anamolous curves 2) Anamolous curves a) Single cotton effect curves a) Single cotton effect curves b) Multiple cotton effect curves b) Multiple cotton effect curves February 11, 2013 26 M.M.C.P.
  • 27.  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 27 February 11, 2013 M.M.C.P.
  • 28. 28February 11, 2013 M.M.C.P.
  • 29.  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. 29 February 11, 2013 M.M.C.P.
  • 30.  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). 30 February 11, 2013 M.M.C.P.
  • 31. 31February 11, 2013 M.M.C.P.
  • 32. Ifthe trough is reached first and the peak it is called a negative cotton effect curves. 32 February 11, 2013 M.M.C.P.
  • 33. TheThe vertical distance between ‘peak’ and ‘trough’ is vertical distance between ‘peak’ and ‘trough’ is called amplitude ‘a’ and is convently expressed in called amplitude ‘a’ and is convently expressed in hundreds of degrees. hundreds of degrees.Molecular amplitude, a =ǿ22 -- ǿ11Molecular amplitude, a =ǿ ǿ 100 100Where,Where, ǿ22 – molar rotation of extreme peak or trough from ǿ – molar rotation of extreme peak or trough from large wavelength. large wavelength. ǿ11 -- molar rotation of extreme peak or trough from ǿ molar rotation of extreme peak or trough from shorter wavelength. shorter wavelength. 33 February 11, 2013 M.M.C.P.
  • 34.  Inthis type of curves two or more peaks and trough are obtained . E.g. functional group i.e. Ketosteriods , Camphor etc exhibits such curves . 34 February 11, 2013 M.M.C.P.
  • 35. 35February 11, 2013 M.M.C.P.
  • 36. Some materials posses special properties of absorption of the leftcirculary polarised light to different extent than the right circularlypolarised light.This phenomenon is called as circularly dichroism.The electric field of a light beam causes a linear displacement ofcharge when interacting with a molecule, whereas the magnetic field of itcauses a circulation of charge.These two motions combined result in a helical displacement whenlight impinges on a molecule (both field vectors in the same place are ofthe same direction but at different moments of time).The magnitude of circular dichroism is expressed by the ellipticiy. 36 February 11, 2013 M.M.C.P.
  • 37. CIRCULAR DICHROISMː – 37February 11, 2013 M.M.C.P.
  • 38. An ordinary spectrophotometer can be adapted to measure circular dichroism. It is only necessary to provide some means of production r and l circularly polarized radiation.For this purpose a plane polarized beam can be passed through a quartz-wave plate. If the plate is rotated from -45o to +45o , first r and l circularly polarized light is produced 38 February 11, 2013 M.M.C.P.
  • 39. 39February 11, 2013 M.M.C.P.
  • 40. APPLICATIONS OF CIRCULAR DICHROISM (CD) SPECTROSCOPYAPPLICATIONS OF CIRCULAR DICHROISM (CD) SPECTROSCOPYPROTEIN CONFORMATION:- PROTEIN CONFORMATION:-The CD spectrum of aaprotein can provide aainformation about the relative amounts of The CD spectrum of protein can provide information about the relative amounts ofthe major types of secondary structure within the protein in solution. the major types of secondary structure within the protein in solution.CD spectra of the α-helix β conformation and the random coil of poly-L-amino acids CD spectra of the α-helix β conformation and the random coil of poly-L-amino acidsare distinctly different form each other. are distinctly different form each other.NUCLEIC ACID CONFORMATION:-NUCLEIC ACID CONFORMATION:-The CD spectrum of aasingle stranded nucleic acid may be calculated fairly accurately The CD spectrum of single stranded nucleic acid may be calculated fairly accuratelyform aaknowledge of its nearest neighbor frequency. Thus any differences between the form knowledge of its nearest neighbor frequency. Thus any differences between thecalculated and measured CD spectrum must be due to variation in structure, such as calculated and measured CD spectrum must be due to variation in structure, such asdouble-strandness. double-strandness.The CD spectra are frequently used to study changes in the structure of nucleic acids The CD spectra are frequently used to study changes in the structure of nucleic acidssuch as: the los of helicity of single stranded nucleic acids as aafunction of temperature such as: the los of helicity of single stranded nucleic acids as function of temperatureor pH structural changes on binding cation and proteins. or pH structural changes on binding cation and proteins. 40 February 11, 2013 M.M.C.P.
  • 41. DIFFERENECES BETWEEN ORD AND CD DIFFERENECES BETWEEN ORD AND CDOPTICAL ROTATORY DISPERSION CIRCUALR DICHROISM(ORD) (CD)ORD is If the refractive indices of the Circular dichroism is the differentialsample for the left and right handed absorption of left and right handedpolarized light are different, when the circularly polarized lightcomponents are recombined , the planepolarized radiation will be rotated throughand angle αORD spectra are dispersive CD spectra are absorptiveIn ORD the circular polarized light is used In CD the circular polarized lgiht is usedis not converted to elliptical light and is converted to elliptical lightORD graphs are obtained by plotting CD graphs are obtained by ploting molarspecific rotation vs wavelength ellipticity vs wavelength. 41 February 11, 2013 M.M.C.P.
  • 42. The octant rule was first formulated by Moffitt et al for correlation of the sign of the cotton effect of chiral cylohexanone derivatives with their absolute configration.The space around carbonyl group is divided into eight sector about x,y,z axis.This rule only applies to substituted cyclohexanone 42 February 11, 2013 M.M.C.P.
  • 43. It states that atoms lying on the back upper left and backIt states that atoms lying on the back upper left and back lower right, then octant make positive contribution. lower right, then octant make positive contribution. (Positive rotation). (Positive rotation).If groups on back upper right and back lower left thenIf groups on back upper right and back lower left then the octants make negative contribution. (Negative the octants make negative contribution. (Negative rotation). rotation).Substituents lying in the co-ordinate planes make noSubstituents lying in the co-ordinate planes make no contribution to the rotatory dispersion. contribution to the rotatory dispersion. 43 February 11, 2013 M.M.C.P.
  • 44. Axial and equatorial group Axial and equatorial groupPositivie cotton effect negativie cotton effectAxial and equatorial group Axial and equatorial group positivenegative cotton effect cotton effect 44 February 11, 2013 M.M.C.P.
  • 45. 45February 11, 2013 M.M.C.P.
  • 46.  If an optically active chromophore takes part in a reaction the extent of the reaction can sometimes be followed by observing the reduction of the cotton effect.Eg:- if hydrochloric acid is added to a solution of (+) 3- methylcyclehexanone in methanol, the cotton effect gets reduced by 93% because of dimethy ketal formation.In alcohol only 33% reduction and in isopropyl alcohol there occurs no reduction. 46 February 11, 2013 M.M.C.P.
  • 47. DeterminationDetermination of position of keto group and the of position of keto group and the confrigration of ring system in a sterodial ketone of confrigration of ring system in a sterodial ketone of unknown constitution. unknown constitution.Study of conformational changes:Study of conformational changes: when molecule exist in more than one confirmation in when molecule exist in more than one confirmation in solution, each conformer will have its own ORD or CD solution, each conformer will have its own ORD or CD curve and the sign and magnitude of the cotton effect curve and the sign and magnitude of the cotton effect will change with the change of conformer population, will change with the change of conformer population, caused either by a change of solvent polarity or by a caused either by a change of solvent polarity or by a change in temperature change in temperature 47 February 11, 2013 M.M.C.P.
  • 48. A. Chetwal GR & Anand SK, Instrumental method of chemical analysis, 5TH edition page no:- 2.468- 2.481.B. Kalsi PS, Spectroscopy Of Organic Compounds, New age international limited, sixth edition:611- 627.C. Jag Mohan, Organic Spectroscopy Principles And Applications, Narosa publishing hose:482- 496.D. Sharma BK, Instrumental method of chemical analysis, 26TH edition:-M-286 to M-307. 48 February 11, 2013 M.M.C.P.
  • 49. 1. What is meant by ORD ? Discuss the principle and application of ORD .(Nov 98).2. What is optical rotatory dispersion & how is it useful in characterization of substances.(Jul 98).3. ORD & Circular Dicroism.(2000).4. Cotton effect .(2004).5. Note on the principle & application of ORD & Circular Dicroism .(2004,Oct 08). 49 February 11, 2013 M.M.C.P.
  • 50. 6. Write an account on fundamental principles of ORD. (2005).7. Explain Circular Dicroism.(2006).8. Describe the instrumentation used for measuring circular dichroism.(Oct 09).9. Explain the phenomena of optical rotation & circular polarization. Giving a schematic diagram, write about an ORD instrument. What are the applications of ORD & CD.(May 10 & 12). 50 February 11, 2013 M.M.C.P.
  • 51. 51February 11, 2013 M.M.C.P.

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