Nmr spectroscopy

basic technique of nmr spectroscopy

1. NMR Spectroscopy Presented to: Dr. Muhammad Irfan Presented by: Aqsa Ayoub FORMAN CHRISTIAN COLLEGE A CHARTERED UNIVERSITY

2. NMR SPECTROSCOPY NMR spectroscopy , is a technique that exploits the magnetic properties of certain atomic nuclei. Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a magnetic field absorb and re-emit electromagnetic radiation. This energy is at a specific resonance frequency which depends on the strength of the magnetic field and the magnetic properties of the isotope of the atoms.

3. Nuclear spin Subatomic particles (electrons, protons and neutrons) can be imagined as spinning on their axes. atoms (such as 12 C) has no overall spin. atoms (such as 1 H and 13 C) has an overall spin. Rules If the number of neutrons and the number of protons are both even, then the nucleus has NO spin. If the number of neutrons plus the number of protons is odd, then the nucleus has a half-integer spin (i.e. 1/2, 3/2, 5/2) If the number of neutrons and the number of protons are both odd, then the nucleus has an integer spin (i.e. 1, 2, 3)

4. In the presence of an applied magnetic field the spin states have different energy and the magnetic moment can align with or against the applied field.  

5. Irradiation of a sample with radio frequency energy corresponding to the spin state separation (DE) will Excite nuclei in the +½ state to the higher energy –½ state afterwards it will loose energy and goes down to ground state and release photon of specific frequency which will be monitored.

6. The radio frequency wave must osscilate with frequency to cause protons to resonate and this frequency is called resonance frequency    

7. Not all protons give resonance signals at the same field frequency. Electrons move in response to the applied field and generate a secondary magnetic field which opposes the applied field. The secondary field shields the nucleus from the applied field N uclei in different environments resonate at different frequencies. The Chemical Shift The difference in resonance frequency is measured as a chemical shift

8. The NMR Spectrometer

9. Number of signals Position of signals (chemical shift ) Relative Intensity of Signals (Integration ) Splitting of signals (spin-spin coupling ) The NMR Graph intensity

10. Spin-Spin coupling Chemical shift of is not only affected by its own electron density but also by neighbouring hydrogen nuclei. Each one of nuclei can spin in either one or two ways: spin up (+1/2) or (-1/2) since there are 2 nuclei there are four possible spin combination that can around the atom (+1/2,+1/2) ,(-1/2,+1/2) ,(+1/2,-1/2) ,(-1/2,-1/2)   1,2 tri bromo ethane same

11. The net magnetic field of can be modified by each one of different combination. Since there are three different chemical shift thus three signals for . The and nuclei are said to be spin-coupled. splitting distance is coupling constants  

12. n + 1 rule Protons in the same environment are said to be equivalent and as such behave as one proton. This follows the n + 1 rule. n is the number of hydrogen atoms attached to the next-door carbon n + 1 is how many peaks will be seen in the cluster.

13. S ummary Nuclei spin(-1/2, +1/2) Magnetic field (two energy states) Chemical shift ( Nuclei in different environments resonate at different frequencies .) Photon emittance (detected) NMR spectra (integration) Spin spin coupling (n+1 rule)

14. Applications of NMR spectroscopy Solution structure Molecular dynamics Protein folding Ionization state Weak intermolecular interactions Protein hydration Hydrogen bonding Drug screening and design Metabolite analysis Chemical analysis