IR and NMR spectroscopy

presentation on absorption spectroscopy

1. Presented by: Asif Mohammad Salehin Jatan Tanchangya Sulov Saha Md . Mohsin Ali

2. Spectroscopy Definition: Spectroscopy is the study of of the interaction between matter and electromagnetic radiation. Types of spectroscopy : Absorption spectroscopy – uses electromagnetic spectra in which a substance absorbs: IR, NMR Emission spectroscopy – uses electromagnetic spectra in which a substance emits: Luminescence Scattering spectroscopy – measures the amount of light that a substance scatter at certain wavelengths, incident angles and polarization angles: Raman

3. Infrared Spectroscopy IR spectroscopy is concerned with the study of absorption of infrared radiation, which causes vibrational transition in the molecule. IR spectra mainly used to identify functional groups present in molecules.

4. Principle of IR spectroscopy Molecules are made up of atoms linked by chemical bonds. The movement of atoms and the chemical bonds like spring and balls (vibration ). This characteristic vibration are called Natural frequency of vibration .

5. When energy in the form of infrared radiation is applied then it causes the vibration between the atoms of the molecules and when, Applied infrared frequency = Natural frequency of vibration

6. Criteria for a compound to absorb IR radiation Correct wavelength of radiation A molecule to absorb IR radiation, the natural frequency of vibrations of some part of a molecule is the same as the frequency of incident radiation. Change in dipole moment A molecule can only absorb IR radiation when its absorption cause a change in its electric dipole.

7. Types of Molecular Vibrations

8. a) Symmetrical stretching: 2 bonds increase or decrease in length simultaneously. H H C

9. b) Asymmetrical stretching: In this, one bond length is increased and other is decreased. H H C

10. a) In plane bending: i. Scissoring ii. Rocking

11. b) Out plane bending: Wagging Twisting H H C C H H C C

12. Instrumentation

13. Interpreting an Infrared Spectrum Ethanoic acid (it contains C-C, C-H, C=O, C-O and O-H bonds.)

14. Fig: IR Spectra of common functional groups

15. Applications Identification of functional group and structure elucidation Identification of substances Studying the progress of the reaction Detection of impurities Quantitative analysis

16. Pros and Cons of IR Spectroscopy

17. NMR Spectroscopy NMR spectroscopy is commonly used technique for organic compound structure determination.

18. Principle of NMR spectroscopy A spinning charge creates a magnetic moment, so these nuclei can be thought of as tiny magnets. If we place these nuclei in a magnetic field, they can line up with or against the field by spinning clockwise or counter clockwise .

19. NMR active nuclei Number of nucleons -Must be odd for residual magnetism For e.g. Hydrogen exhibits, Deuterium does not 1 H , 13 C and 15 N nuclei have a very small magnetic moment: “half integer spin ”

20. Resonance condition Transition from low to high energy state occurs h ﬠ = gßH Either a constant magnetic field is applied and appropriate region of r adio f requency is swept Or a constant frequency is employed & the external magnetic field is swept

21. Chemical shifts Arises from applied field inducing secondary fields at the proton by interacting with adjacent bonding electrons Is measured in ppm relative to an internal standard – TMS Trimethylsilane (TMS) is the accepted internal standard for calibrating   chemical shift  for 1H, 13C and 29Si NMR spectroscopy in organic solvents. H 3.6 ppm 1.2 ppm

22. Splitting or Multiplicity Scalar coupling constants - P rotons on adjacent carbons will interact and “split” each others resonances into multiple peaks ( multiplets ) Measured in Hz ( “ Hertz ” , s -1 ) Caused by different spin states of neighboring spins (parallel or antiparallel) H Equivalent protons do not show spin-spin coupling Doublet : 1 coupling partner Triplet: 2 coupling partners Quartet: 3 coupling partners

23. Steps involved in the process

24. Instrumentation

25. Fourier Transform NMR Instrument Continuous Wave NMR Instrument Two types of NMR spectroscopy instruments

26. 1 H NMR Spectroscopy

27. Study of 1 H NMR Spectra

28. 13 C NMR Spectroscopy

29. Interpretation of NMR Spectrum Number of main signal = number of equivalent protons in unknown compound Chemical shift indicates the type of H atoms. E.g. methylene, methyl groups, etc. Spin-spin splitting ---- arrangement of groups in the molecule. Area of peaks ---- no. of H nuclei present in each group. For e.g. relative areas of methyl peaks in propane would be 6:2. In butane it would be 6:4

30. E.g. of ethanol a) Low resolution spectrum b) High resolution spectrum

31. Applications To study molecular structure and interactions For determining 3D structure of proteins and other macromolecules Solid-state NMR is used to study variety of materials Magnetic Resonance Imaging (MRI) Oil and natural gas exploration Polymer production, cosmetics and food manufacturing

32. ppm H 2 O Protein NMR

33. MRI Eliminates risk of X-radiation Excellent and contrast resolution Detecting disease at earlier stages Magnetic resonance imaging ( MRI ) is a noninvasive medical test that physicians use to diagnose and treat medical conditions.

34. Pros and Cons of NMR Spectroscopy