Application of ir

1. APPLICATIONS OF INFRA-RED SPECTROSCOPY By, Joan Vijetha.R M.Pharm (Pharmaceutics ) 1

2. CONTENT Introduction Application of IR Qualitative analysis Quantitative analysis Summary 2

3. INTRODUCTION Sufficient information about the structure. Large no. of absorption band from which a wealthy information about the structure can be derived. Radiation causes the molecules to stretch or bend with respect to one other. 0.8-2.4µ/12500-4000cm -1 -Near Infra Red 2.5-15µ/4000-667cm -1 - Mid Infra Red 15-200µ/667-50cm -1 -Far Infra Red Principle -Excitation of molecule from lower to higher vibrational level 3

4. Qualitative analysis Used for identifying organic, inorganic, and biological species . The time required to perform a structural determination was reduced by a factor of ten, one hundred, or even one thousand (by FTIR modern instruments ). Identification of an organic compound is a two-step process. The first step involves determining what functional groups are most likely present by examining the group frequency region. The second step then involves a detailed comparison of the spectrum of the unknown with the spectra of pure compounds that contain all of the functional groups found in the first step. 4

5. The fingerprint region, from 1200 to 7 00 cm -1 is particularly useful because small differences in the structure and constitution of a molecule result in significant changes in the appearance and distribution of absorption peaks in this region . 5

6. Identification of functional group A large number of compound can be estimated by knowing the functional group. 6

7. 7 m=medium, w=weak, s=strong, n=narrow, b=broad, sh =sharp

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9. Methyl salicylate 9

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15. Study of keto-enol tautomerism Diketones and ketoester exhibit keto-enol tautomerism provided they have α-H atom in them. Acetoacetic ester-exists in keto enol isomers in equilibrium 15

16. Study of complex molecules Used to establish the structure of complex molecules Eg : Two structure of penicillin were proposed on basis of IR * The IR spectra of oxazolones shows 2 banbs 1825 and 1675 cm -1 but no such band appeared in spectrum of penicillin so, oxazolones structure was ruled out. * ẞ lactaum ring do not absorb near 1770cm -1 But ẞ lactaum when fused with thiazolidin ring exhibits a band at 1770cm -1 16

17. Study of conformational analysis Used to determine the relative stability of various conformational of cyclic compound. Eg : In cyclohexane both chair and boat form exist They are stable in both the form. As per IR selection rules there 18 active C-C and CH2 rocking & twisting is possible for boat form . As per IR selection there are five band for chair form . The spectral examination cyclohexane region is near1350-700cm -1 reveals 5 band for chair form hence more stable. 17

18. Geometrical isomerism Vibration in IR is caused by change in dipole-movement. Also the absorb depend upon the change in dipole-movement. This technique clearly makes a distinction between cis and trans isomers. Eg : 1,2-dichloro ethene In trans isomers no dipole occur so no peak But in case of cis dipole movement occur so peak form at 1580cm -1 18

19. Rotational isomerism IR spectroscopy helps in the detection of skew(gauche) and trans( staggerd ) conformation. Eg:1,2 dichloro ethane. Two bands at 1291 and 1235cm -1 Trans form predominates at low temperature. Skew at higher temperature. 19

20. Identity by Fingerprinting Each compound has a different and unique characteristic set of adsorption band in spectrum. 7 00-1400cm -1 is called fingerprint region. To identify the unknown compound one need to compare with the standard spectra record. Substance that give same IR spectra are identical. Small differences in the structure and constitution of a molecule result in significant changes in the distribution of absorption peaks . As a consequence, a close match between two spectra in this fingerprint region constitutes strong evidence for the identity of compounds yielding the spectra . Exact interpretation of spectra in this region is seldom possible because of the complexity of the spectra. 20

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23. Study of hydrogen bonding IR spectroscopy is a power full and widely used method for studying hydrogen bonding. Hydrogen bonding alter the vibration frequencies of OH and NH group. An inert simple alcohol exhibits a sharp absorption at 3620-3640cm -1 and broad at 3500-3200cm -1 . As solution dilution increases sharp peak is obtained. The sharp absorption at higher wave length is due to OH stretching. It becomes more intense at higher dilution because association of solute molecules is less probable. 23

24. At higher concentration they form dimers, trimers and polymers and so it gives broad peaks. Intermolecular hydrogen bonding decrease with dilution, where as interamolecular hydrogen bonding shows no effect. 24

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26. Progress of reactions By this method the progress of the reaction can be followed. By examination of the small portion of the spectrum is sufficient to indicate if the product has been formed or not. Eg : Oxidation of secondary alcohol by chrominum (VI) is accompanied by decreases in the absorption intensity of OH group. 26

27. Detection of impurity This can be done by comparing the standard and the test spectrum. Pure sample consist of a sharp peak and impure consist of bent one and also some additional band . 27

28. QUANTITATIVE ANALYSIS The quantity of the substance can be determined either in pure form or as a mixture of two or more compounds. In this, characteristic peak corresponding to the drug substance is chosen by of peaks for standard and test sample is compared. This is called base line technique to determine the quantity of the substance.   28

29. 29 There are few difficulties in using this method Deviation from Beer's law Determination of single analytic concentration in a mixture. The absorption band of a group in a compound is never symmetrical

30. A typical band: C A D B By applying Beer’s law, the concentration can be determined   30

31. Application of NIR Has been widely used in analysis of agriculture, food and pharmaceutical products. It is a rapid technique and also adapted to quality control of streams as, optical fiber, remote sampling in industrial environment is possible. Mostly useful in determination of solid material. 31

32. Application of Fir Mostly use in treatment of disease and illness. These rays are totally visible to our naked eyes, capable of penetrating deep into human body. Also used to observe interstellar gases. 32

33. Summary There are two main application of IR qualitative & quantitative. The determination of the functional group, structural determination , Progress of reactions, geometrical isomers, Study of hydrogen bonding, ect ,. The application of near IR, mid IR & far IR. Near IR- Agriculture , food and pharmaceutical products . Mid IR- Organic , inorganic, and biological species. Far IR- Treatment of chronic health , observe interstellar gases. 33

34. Reference William kemp -Organic spectroscopy, page no.-55-58. R.Gopalan , PS Subramaniam , K.Rengarajan , Elements of analytical chemistry, 3 rd edition 2003, page no-244-249. D.Kealey and PJ Haines, Analytical chemistry, 1 st edition-2002, page no-245-247. R Gurdeep Chatwal,K Sham Anand , Instrumental method of chemical analysis, 7 th edition-2007, page no-2.73-2.74. YR Sharma, Elementry organic spectroscopy, page no-89,137-140. 34

35. 35 THANK YOU