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  • 1. :UV-Vis Spectroscopy Dr. Mahwish QayyumOrganic Spectral Analysis1

2. Welcome to My Class! Dr.Mahwish Qayyum 3. Table of contents introductionUV & electronic transitionsUsable ranges & observations Selection rules Band Structure Instrumentation & Spectra Beer-Lambert Law Application of UV-spec Conclusion 4. 513PHARMACEUTICAL CHEMISTRY-III (Instrumentation-I) Cr. Hr. 03Topics include: 5th Semester513 PHARMACEUTICAL CHEMISTRY-III (Instrumentation-I) (Theory) Cr. Hr. 03 Note:- The topics will be taught with special reference to their Pharmaceutical Applications. Theory, Instrumentation and Pharmaceutical Applications of the following Spectroscopic Methods 1. Atomic Absorption and Emission Spectroscopy. 2. Molecular fluorescence spectroscopy. 3. Flame Photometry. 4. I.R. Spectroscopy. 5. Mass Spectroscopy. 6. NMR Spectroscopy. 7. UV/Visible Spectroscopy 515 PHARMACEUTICAL CHEMISTRY-III (Instrumentation-I) (Laboratory) Cr. Hr. 01 NOTE:- Practical of the subject shall be designed from time to time on the basis of the above mentioned theoretical topics and availability of the requirements, e.g. Determination of the Purity and Composition of the unknown drugs by using at least each of the above techniques . 5. Reference books PHARMACEUTICAL CHEMISTRY-III (Instrumentation-I) 5th ( Semester) Lough W J, High Performance Liquid Chromatography, Blacki Academic Press, New York, 1996. William Kemp,Organic Spectroscopy, Ellsi Horwood, London, 1990. M Aminuddin & Javed Iqbal, Theory and Practice of Chromatography,University Grants Commission, Islamabad-Pakistan (2000). A H Beckett and J B Stennlake, Practical Pharmaceutical Chemistry,Part I and II, the Aulton Press, London. A M Knevel and F E Digangi, Jenkinss quantitative Pharmaceutical Chemistry, McGraw-Hill Book Company, New York. Braithwaite and F J Smith, Chromatographic Methods, Chapman andHall, London. E Heftmann, Chromatography, Von Nostrond Reinheld Co, New York,1975. Pryde and M J Gilbert, Applications of High Performance Liquid Chromatography, Chapman & Hall, London, 1979. E Stahl, Thin Layer Chromatography, Springer-Verlag, Berlin, 1969. 10. R Hamilton, Introduction to HPLC, P A Sewell, Chapman & Hall, London, 1982. Organic chemistry by M.YOUNIS 6. Our Classroom Rules 1 No food in the classroom (unless it's cake/chocolate for me)any confusion then refer to rule 2 again 3.Avoid death by powerpoint so no sleep otherwise its going to be sleep forever 4.Avoid commenting about anything in your paper chat coz save your self by not providng documented proofs (personal experience) 5.Only smarter questions are allowed (Watch out ahsan) 6.Theres a difference in a classroom & common room 7. Pleasee don't refresh your gloss or your hair by facing it towards your teacher face assuming it as a mirror (God you really wanna do that !!! DaAA) 2 Teacher is always correct if you find have 7. We are going to have a wonderful semester of learning! InshAllah sooooo 8. Lets start with the name of great Almighty AllahO My Lord! expand my chest for me. And ease my task for me; and loose a knot from my tongue, (That) they may understand my saying. (20:25-2) 9. SpectroscopySpectroscopy is a general term referring to the interactions of various types of electromagnetic radiation with matter. Exactly how the radiation interacts with matter is directly dependent on the energy of the radiation. 10. The molecular spectroscopy is the study of the interaction of electromagnetic waves and matter. The scattering of suns rays by raindrops to produce a rainbow and appearance of a colorful spectrum when a narrow beam of sunlight is passed through a triangular glass prism are the simple examples where white light is separated into the visible spectrum of primary colors. This visible light is merely a part of the whole spectrum of electromagnetic radiation, extending from the radio waves to cosmic rays. All these apparently different forms of electromagnetic radiations travel at the same velocity but characteristically differ from each other in terms of frequencies and wavelength 11. Early days of medicinal chemistry i)2 major problems Separation of a chemical substance either from mixture/natural sourceii)Chemical analysis bothqualitativeand quantitativeiii) Early days qualitative (sublimation, crystallization, distillation etc) iv) Quantitative (volumetric/gravimetric)v) Electromagnetic radiations can also give information i.e empirically to presence of certain functional groups.so can help in structural and analytical 12. Electromagnetic radiation: Transmission of energy radiant energy Heat and light energy Quantum mechanics suggests that e.m radiation dual nature Waves Particle like discrete packets energy 13. UV SpectroscopyI.Introduction A. UV radiation and Electronic Excitations1.2.This energy corresponds to EM radiation in the ultraviolet (UV) region, 100-350 nm, and visible (VIS) regions 350-700 nm of the spectrum For comparison, recall the EM spectrum:-raysX-raysUVIRMicrowaveRadioVisible3. 4. 5.RAMIVISUALIZES ULTRA XRAYS GA CARUsing IR we observed vibrational transitions with energies of 8-40 kJ/mol at wavelengths of 2500-15,000 nm For purposes of our discussion, we will refer to UV and VIS spectroscopy as UV13 14. Spectroscopy Utilises theAbsorption and Emission of electromagnetic radiation by atomsAbsorption: Low energy electrons absorb energy to move to higher energy levelEmission: Excited electrons return to lower energy states15 15. Absorption v. EmissionEnergy is emitted by electrons returningto lower energy levels3rd Excited States2nd1stEnergy is absorbed as electrons jump to higher energy levels Ground State16 16. Absorption Spectra Sodium18 17. The Spectroscopic Techniques are based on the fact thatLight absorbed(Absorption)is directly proportional to theConcentration19of the absorbing component. 18. A FLASH BACK !!!!!!!!!20 19. UV-Visible Spectroscopy A UV-visible spectrophotometer measures the amount of energy absorbed by a sample.21 20. The optics of the light source in UV-visible spectroscopy allow either visible [approx. 400nm (blue end) to 750nm (red end) ] or ultraviolet (below 400nm) to be directed at the sample under analysis.22 21. 23 22. Why are carrots orange? Carrots contain the pigment carotene which absorbs blue light strongly and reflects orange red and so the carrot appears orange.400nm500nmBLUE420nm600nmGREEN520 nm24700nmY E L LO WO R A N G E600nmRED 23. Carotene beta-Carotene forms orange to red crystals and occurs in the chromoplasts of plants and in the fatty tissues of plant-eating animals. Molecular formula: C40H56 Molar Mass 537 Melting point 178 - 179 C25 24. Absorbance is set to 0% or light transmitted using a solvent blank in a cuvet. This compensates for absorbance by the cell container and solvent and ensures that any absorbance registered is solely due to the component under analysis.The sample to be analysed is placed in a cuvetQualitative analysis is achieved by determining the radiation absorbed by a sample over a range of wavelengths. The results are plotted as a graph of absorbance/transmittance against wavelength, which is called a UV/visible spectrum.26 25. The UV- Visible absorption spectrum for carotene in the non-polar solvent, hexane I NT EN S I TY O F A B S O R P T I O N700 nm400nmultra- violet320nm27visible460nm540nminfrared 26. Although the light absorbed is dependent on pathlength through the cell, a usual standard 1cm pathlength is used so that pathlength can effectively be ignored. Quantitative analysis is achieved in a manner similar to colorimetry. The absorption of a sample at a particular wavelength (chosen by adjusting a monochromator) is measured and compared to a calibration graph of the absorptions of a series of standard solutions.What can be analysed?In its quantitative form, UV-visible spectroscopy can be used to detect coloured species in solution eg. bromine , iodine and organic compounds or metal ions that are coloured, or can be converted into a coloured compound. 28 27. Molecular orbital is the nonlocalized fields between atoms that are occupied by bonding electrons. (when two atom orbitals combine, either a low-energy bonding molecular orbital or a high energy antibonding molecular orbital results.) Sigma ( ) orbital The molecular orbital associated with single bonds in organic compounds Pi ( ) orbital The molecular orbital associated with parallel overlap of atomic P orbital. n electrons No bonding electrons 28. UV SpectroscopyI.IntroductionB. C.The Spectroscopic Process The difference in energy between molecular bonding, non-bonding and anti-bonding orbitals ranges from 125-650 kJ/mole1. 2. 3. 4.In UV spectroscopy, the sample is irradiated with the broad spectrum of the UV radiation If a particular electronic transition matches the energy of a certain band of UV, it will be absorbed The remaining UV light passes through the sample and is observed From this residual radiation a spectrum is obtained with gaps at these discrete energies this is called an absorption spectrum30 29. UV SpectroscopyI.Introduction C. Observed electronic transitions 1. The lowest energy transition (and most often obs. by UV) is typically that of an electron in the Highest Occupied Molecular Orbital (HOMO) to the Lowest Unoccupied Molecular Orbital (LUMO)2.3.For any bond (pair of electrons) in a molecule, the molecular orbitals are a mixture of the two contributing atomic orbitals; for every bonding orbital created from this mixing ( , ), there is a corresponding anti-bonding orbital of symmetrically * * higher energy ( , ) The lowest energy occupied orbitals are typically the anti-bonding orbital is of the highest energylikewise, the corresponding-orbitals are of somewhat higher energy, and their complementary anti-bonding orbital somewhat lower in energy than *.5.Unshared pairs lie at the energy of the original atomic orbital, m