UV spectroscopy ppt.

UV spectroscopy ppt

1. Factors affecting the position and intensity of UV bands – effect of conjugation, steric factor, pH, and solvent polarity. Presented by :- Aniket Bhagwan suryawanshi Class:- M.Sc part 1
Subject :- Organic chemistry
Roll no :- 22216019 1.

2. Content Introduction The visible spectrum UV spectroscopy use Effect of Conjugation Steric Factor and Ph Solvent Polarity Reference Acknowledgement 2.

3. Introduction Ultraviolet–visible (UV–visible) spectrophotometry is primarily a quantitative analytical technique concerned with the absorption of near-UV (180–390 nm) or visible (390–780 nm) radiation by chemical species in solution. A molecule contains electronic, vibrational and rotational energy levels. Each electronic level. Within a molecule, in associated with a number of vibrational levels with less energy separations and each Vibrational level in turn is associated with a set of rotational levels with even less energy separation as shown in the Fig. 3.1. 3.

4. The visible spectrum 4.

5. Why we use UV – Spectroscopy ? 1. Detection of functional groups.
2. Detection of impurities 3. Qualitative analysis
4. Quantitative analysis
5. Single compound without chromophore
6. Drugs with chromophoric reagent 7. It is helps to show the relationship between different groups, it is useful to detect the conjugation of the compounds. 5.

6. Effect of Conjugation The ultraviolet absorption maximum of a conjugated molecule is dependent upon the extent of conjugation. When a molecule absorbe uv -visible radiators, the electon Excites from its HOMO to LUMO. The energy difference between these two levels decided the wavelength of maximum absorption. 1. H2C=CH2 Ethylene λmax :- 175nm 6. 2.CH₂=CH-CH=CH₂ 1,3 butadiene λmax :- 217nm

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8. Effect of conjugation of alkenes (Bathochromic shift) The energy gap for a π - π* transition becomes increasingly narrow, and the wavelength of light absorbed correspondingly becomes longer. Extention of conjugation leads to both Bathochromic shift and hyperchromic effect The energy of a photon  is given by 8.

9. Here, we see that the extended system of conjugated pi bonds causes the molecule to absorb light in the visible range. Because the  λ max  of 524 nm falls within the green region of the spectrum, the compound appears red to our eyes. 9.

10. Here, maximum absorbance is at 630 nm, in the orange range of the visible spectrum, and the compound appears blue. 10.

11. Effect of solvent Polar solvents such as water and alcohol forms hydrogen bond with polar molecules (shifts in absorption bands). A dilute solution of the sample is always prepared for spectral analysis. Most commonly used solvent is 95% ethenol . Polar solvents stabilises/destabilises the molecular orbital and changes the energy level of ground state or excited state of the molecule (alters the energy gap). 11.

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13. Hexane and other hydrocarbons can be used because these are less polar and have least interacti on with the molecule under investigation. The position as well as the intensity of absorption maximum get shifted for a particular chromopore by changing the polarity of the solvent. By increasing the polarity of the solvent, compounds such a dienes and conjugated hydrocarbon do not experience any appreciable shift. 13.

14. Effect of Steric hindrance 14.

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16. Effect of PH sample solution 16.

17. Examples:- 17.

18. Solvent Polarity A solvent which does not itself absorb in the region under investigation is the most suitable solvent for UV-visible spectroscopy. Most commonly used solvents are 95% EtOH , H 2 O and hexane.   It has been observed that the intensity as well as the λ max  shift with the change of the polarity of the solvent.  The value of absorption maximum for non-polar compound is same in ethanol (polar Compund ) and hexane (non-polar Compund ).  18.

19. Transition Solvent Shift * Polar Non-Polar Bathochromic Shift Hypsochromic Shift n * Polar Non-Polar Hypsochromic Shift Bathochromic Shift Transition Solvent Shift Polar Non-Polar Bathochromic Shift Hypsochromic Shift Polar Non-Polar Hypsochromic Shift Bathochromic Shift 19.

20. Effect of solvent polarity in Absorption spectra 20.

21. Reference Organic Spectroscopy, V.R. Dani, Tata McGraw Hill Publishing Co. Spectroscopy of Organic Compounds, P.S. Kalsi , New Age International Ltd. Spectrometric Identification of Organic Compounds, R. Silverstein, G.C Bassler and T.C. Morrill, John Wiley and Sons. 21.

22. Acknowledgement Name of College : ICLE’S Motilal Jhunjhumwala College
Name of the Department : Chemistry
Head of the Department : Dr. Aruna Sharma Madam
Name of the Guide : Dr. Sonali Thakare Madam 22.

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