2. Contents.
➢ Introduction.
➢ NMR theory.
➢ Principle of NMR.
➢ Larmor precession.
➢ Larmor frequency.
➢ CHEMICAL SHIFT.
➢ Shielded proton.
➢ Deshielded proton.
➢ Factors affecting chemical shift.
➢ NMR SPECTRUM.
➢ Coupling.
➢ Pascal Triangle
➢ Relaxation process in NMR.
➢ Instrumentation.
➢ Working.
➢ Applications.
3. Introduction
➢ Spectroscopy . It is a study of interaction of electromagnetic radiation with the
matter.
➢ Nuclear Magnetic resonance spectroscopy, most commonly known as NMR
spectroscopy.
➢ Nuclear magnetic resonance NMR is a spectroscopy technique which is based on
the absorption of electromagnetic radiation in the radio frequency region 4 to 900
MHz by the nuclei of the atoms.
➢ Spectroscopy determines the physical and chemical properties of atoms or the
molecule in which they are contained and provide detailed information about the
structure, dynamics ,reaction and chemical environment of the molecule.
➢ It is used to study wide variety of nuclei.
➢ 1H
➢ 15N
➢ 19F
➢ 13C
➢ 31P
4. Spin quantum number related to atomic and mass number of
nuclei.
Elements with odd atomic and mass number have the property
of nuclear spin,.
NMR theory
5. If the external magnetic field is applied the number of possible orientation are given by.(2I +1).
HYDROGEN HAS SPIN QUANTUM NUMBER I= ½.And the possible orientation is 2 = ½ ,_1/2.
6. ➢ Principle of NMR is based on spinning of nucleus
and generating magnetic field.
➢ Without external magnetic field Bo the nuclear
spin are random in direction.
➢ With Bo the nuclear spin align themselves either
along or against the field of external magnetic
field
PRINCIPLE OF NMR.
7. ➢ If an external magnetic field is applied the energy transfer is possible between ground state
to excited state.
➢ When spin return to its ground state level absorbed radio frequency energy is emitted at the
same frequency level.
➢ the emitted radiofrequency signal that gives the NMR spectrum of concerned nucleus and
is directly proportional to the strength of applied field.
8. Larmor precession
➢ Larmor precession (named after Joseph Larmor) is the precession of the magnetic moment of an
object about an external magnetic field.
➢ The phenomenon is conceptually similar to the precession of a tilted classical gyroscope . Objects with
a magnetic moment also have angular momentum and effective internal electric current proportional to
their angular momentum.
➢ The external magnetic field exerts a torque on the magnetic moment,
9. Larmor frequency
➢ The Larmor or processional frequency refers to the rate of precession of the magnetic moment of the
proton around the external magnetic field.
ω = γB.
➢ where ω is the Larmor frequency in MHz, γ is the gyromagnetic ratio in MHz/tesla and B is the strength
of the static magnetic field in tesla.
➢Gyromagnetic ratio γ = magnetic dipole/angular momentum
➢Gyroscope:
10. Chemical shift.
Chemical shift is a difference in the resonate frequency of the two nuclei due to differences in there local
molecular environment. OR the difference between the resonate frequency of the observed nucleus and the
reference TMS. Chemical shift is denoted by the symbol (δ) and is measured in ppm (parts per million).
Shielding of proton .High electron density around the nucleus shield he nucleus from the external
magnetic field and the signals are up field in the NMR spectrum.
11. Deshielding of proton.
Lower electron density around the nucleus Deshields the nucleus from the external magnetic
field and the signals are downfield in NMR Spectrum.
12. Factors affecting chemical shift
➢ Electronegative group.
➢ Hydrogen bonding
➢ Vander Waals deshelling.
➢ Effect of temperature and effect of solvent.
Electronegative group. Electronegative group attached to the C-H system decreases the electron density
around the proton. And there is less shielding and chemical shift increases.
13. ➢ Vander Waals deshieding.
➢ The electron cloud of a bulkier group will tend to repel the electron cloude surrounding the proton .such
proton will be Deshields and will resonate at slightly higher value of chemical shift then expected in the
absence of this effect,
➢ Effect of temperature. Resonance position of most signals is little effected by temperature.
➢ Effect of solvent. Chemical shift when the solvent changed from ccl4 to cdcl3 is 0.1ppm.but the change
to more polar solvent like methanol change is 0.3 ppm. Solvent used in NMR ccl4,CDCL3,D2O.
➢ HYDROGEN BONDING.
➢ PROTON that are involved in hydrogen bonding are typically change the chemical shift values.
➢ The more hydrogen bonding the more proton is deshelled and chemical shift value is higher.
14. NMR Spectrum
NMR spectrum is a plot of intensity of NMR signals vs magnetic field frequency in reference to TMS.
15. Coupling
➢ The spinning hydrogen nuclei in a molecule will interact with each other and cause the signal in the NMR
peak to split.
➢ The separation distance between two adjacent peaks, as a result of the spin-spin interaction , is constant
and is known as coupling constant (denoted by the letter J).
16. Pascal Triangle
The Pascal’s triangle is a graphical device used to predict the ratio of heights of lines in a split NMR peak.
17. Relaxation process.
➢ NMR relaxation is the processes by which an excited magnetic state returns to its equilibrium distribution oR
Relaxation is the process in which spins release the energy received from a radiofrequency pulse.
➢ The two types of NMR relaxation time is the
➢ spin-lattice relaxation time (T1)
➢ the spin-spin relaxation time (T2).
19. ➢Working
➢ In NMR the sample is dissolved in CCL3 and placed in a magnetic field. The radio frequency
generator irradiated the sample with the radiation. When nuclei fall back to lower energy states.
Detector measure the energy released and spectrum is recorded. The super conducting magnet in
modern NMR Spectrophotometer have a coil that are cooled in liquid helium and conduct
electricity.
20. Application.
➢ NMR used for the structure elucidation oof organic and inorganic solids.
➢ Determines physical and chemical property of atoms.
➢ Application in medicine.
➢ Measuring physiological function.
➢ Flow measurement nd angiography.
➢ Tumours
➢ MRI.
➢ Brain.
➢ Distinguish white and grey matter.
➢ Detect tumours ,haemorrhage.
21.
22. conclusion
The NMR spectroscopy determines the physical and chemical properties of atoms or molecules. It relies
on the phenomenon of nuclear magnetic resonance and provides detailed information about the
structure, dynamics, reaction state, and chemical environment of molecules. Apart from the molecular
structure, NMR spectroscopy can determine phase changes, conformational and configurational
alterations, solubility, and diffusion potential .
