Ir spectroscopy

The presentation is all about infrared spectroscopy

1. IR Spectroscopy (Infrared)

2. 3D Animation of IR Molecular vibrations https://drive.google.com/file/d/1XxjDZwEVCLDfWprSSgxqk2Ld-uPvmWx3/view?usp=sharing

3. Animation of IR Molecular vibrations https://drive.google.com/file/d/1VWSk7yoLL3UpcZAI5xExKl622Wx0aYy1/view?usp=sharing

4. SAMPLE HANDLING OR SAMPLING TECHNIQUES

5. SAMPLE HANDLING OR SAMPLING TECHNIQUES 4 types of sampling techniques Solid sampling liquid sampling gas sampling Solution sampling

6. SOLID SAMPLING Direct sampling Pellatization technique Mulling technique Solution technique

7. DIRECT SAMPLING POWDERED SOLID POWDER IS TAKEN IN SAMPLE HOLDER AND PLACED IN THE IR SPECTROPHOTOMETER AND ANALYZED.

8. PELLATIZATION TECHNIQUE KBr NaCl These are used for preparation of pallets with sample. Both are transparent for IR radiations

9. MULLING TECHNIQUE Preparation of Mull (paste) Mulling agents are used e.g. Nujol (High molecular weight liquid like paraffin) Hexachlorobutadiene Chlorofluorocarbon MULL = NUJOL + SAMPLE

10. SOLUTION TECHNIQUE Sample should be volatile Addition of Potassium bromide to sample

11. LIQUID SAMPLING Sample is sandwitched between two sodium chloride pellets or layers

12. GAS SAMPLING Gas cells are used Length of gas cells are 10 cm It is made up of sodium chloride

13. SOLUTION SAMPLING Chloroform Carbontetrachloride Carbon disulphide These are used to dissolve various samples Now sample is analyzed in form of solution

14. FACTORS AFFECTING VIBRATIONS

15. FACTORS AFFECTING VIBRATIONS There are four factors which affects vibrations in IR spectroscopy 1. Coupled vibration 2. Fermi resonance 3. Electronic effect 4. Hydrogen bonding

16. Coupled vibrations – Example – i. C-H stretching – one vibrational frequency ii. If CH 2 (Methylene group) – Two absorption frequencies (Symmetrical and Asymmetrical) Symmetrical – Lower wave number and Asymmetrical – Higher wave number

17. Fermi resonance – Overtone band – spectral band occurs in vibrational spectrum of a molecule when the molecules makes transition from ground state to excited state. This gives rise to resonance and known as Fermi resonance. Due to Fermi resonance wave number increases.

18. Electronic effect Absorption frequency will change when there is change in the substituents of the neighbouring group. Due to electronic effect. Various electronic effects occurs i. Inductive effect - +I (Wave number decreases) & -I (Wave number increases) ii. Mesomeric effect – wave number decreases iii. Field effect – wave number either increases or decreases

19. Hydrogen bonding Due to hydrogen bonding wave number decreases Example – N-H-----N-H (N-H = 3500 cm -1 before hydrogen bonding whereas N-H = 3300 cm- 1 after hydrogen bonding) O-H---O-H (O-H = 3600 cm -1 before hydrogen bonding whereas O-H = 3450 cm -1 after hydrogen bonding)

20. INSTRUMENTATION

21. IR SPECTROPHOTOMETER PARTS

22. SOURCE OF RADIATION

23. SOURCE OF RADIATION INCANDESCENT LAMP NERNST GLOVER GLOBAR SOURCE MERCURY ARC LAMP TUNSTEN FILAMENT LAMP

24. NERNST GLOWER

25. GLOBAR SOURCE

26. MERCURY ARC LAMP

27. DETECTORS

28. DETECTOR Detectors act as photon transducers, which transform electromagnetic radiation into electrical signals which can be amplified and processed for final interpretation. Golay cell Bolometer Thermocouple Thermistor Photoelectric detector

29. GOLAY CELL The Golay cell is a detector used in infrared spectroscopy . It consists of a gas-filled enclosure with an infrared absorbing material and a flexible diaphragm or membrane. When infrared radiation is absorbed, it heats the gas, causing it to expand. The resulting increase in pressure deforms the membrane. Light reflected off the membrane is detected by a photodiode , and motion of the membrane produces a change in the signal on the photodiode. The Golay cell has high sensitivity.

30. BOLOMETER A bolometer is a device for measuring the power of incident electromagnetic radiation via the heating of a material with a temperature-dependent electrical resistance .

31. ANIMATION - WORKING OF IR SPECTROPHOTOMETER https://www.youtube.com/watch?v=OiukFtC8E04

32. APPLICATIONS OF IR SPECTROSCOPY

33. APPLICATIONS OF IR SPECTROSCOPY Infrared spectroscopy is widely used in industry as well as in research. It is a simple and reliable technique for quality control and measurement.

34. 1. Identification of functional group and structure elucidation Entire IR region is divided into group frequency region and fingerprint region. Range of group frequency is 4000-1500 cm -1 while that of fingerprint region is 1500-400 cm -1 . In group frequency region, the peaks corresponding to different functional groups can be observed.

35. According to corresponding peaks, functional group can be determined. Each atom of the molecule is connected by bond and each bond requires different IR region so characteristic peaks are observed. This region of IR spectrum is called as fingerprint region of the molecule. It can be determined by characteristic peaks.

36. 2. Identification of substances IR spectroscopy is used to establish whether a given sample of an organic substance is identical with another or not. This is because large number of absorption bands is observed in the IR spectra of organic molecules and the probability that any two compounds will produce identical spectra is almost zero. So if two compounds have identical IR spectra then both of them must be samples of the same substances. IR spectra of two enatiomeric compound are identical. So IR spectroscopy fails to distinguish between enantiomers.

37. For example, an IR spectrum of benzaldehyde is observed as follows. C-H stretching of aromatic ring- 3080 cm -1 C-H stretching of aldehyde- 2860 cm -1 and 2775 cm -1 C=O stretching of an aromatic aldehyde- 1700 cm -1 C=C stretching of an aromatic ring- 1595 cm -1 C-H bending- 745 cm -1 and 685 cm -1 No other compound then benzaldehyde produces same IR spectra as shown above .

38. 3. Studying the progress of the reaction Progress of chemical reaction can be determined by examining the small portion of the reaction mixure withdrawn from time to time. The rate of disappearance of a characteristic absorption band of the reactant group and/or the rate of appearance of the characteristic absorption band of the product group due to formation of product is observed.

39. 4. Detection of impurities IR spectrum of the test sample to be determined is compared with the standard compound. If any additional peaks are observed in the IR spectrum, then it is due to impurities present in the compound.

40. 5. Quantitative analysis The quantity of the substance can be determined either in pure form or as a mixure of two or more compounds. In this, characteristic peak corresponding to the drug substance is chosen and log I0/It of peaks for standard and test sample is compared. This is called base line technique to determine the quantity of the substance.

41. TAPAN KUMAR MAHATO [email protected]