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1. MET FACULTY OF PHARMACY PRESENTATION ON NUCLEAR MAGNETIC RESONANACE SUBMITTED BY: ANSHIKA BHATNAGAR M.PHARMA FIRST YEAR (PHARMACEUTICAL CHEMISTRY)

2. TABLE OF CONTENT: Introduction Principle of Nuclear Magnetic Resonance Quantum number and their rules in NMR Instrumentation of NMR Solvent requirement in NMR Relaxation Process NMR signals in Various compounds Chemical shift and Factors influencing chemical shift Spin -Spin coupling Coupling constant

3. INTRODUCTION Nuclear magnetic resonance (NMR) spectrometry is another form of Absorption spectrometry in which radio frequency waves induce transitions between magnetic energy levels of nuclei of a molecule. All nuclei carry a charge. In some nuclei this charge spins on the nuclear axis and this circulation of nuclear charge generates a magnetic dipole along the axis. The angular momentum of the spinning charge can be described in terms of quantum spin numbers. Radio waves are the lowest energy form of electromagnetic radiation and it can be seen that the quantity of energy involved in rf radiation is very small which is too small to vibrate, rotate or excite an atom or molecule. But this energy is sufficient to affect the nuclear spin of the atom of a molecule.

4. PRINCIPLE OF NMR The above figure showing the nucleus in Absence and Presence of External Magnatic field

5. CONTINUE NMR is based on the spins of atomic nuclei. Two possible orientation means nucleus can either aligned with the applied magnetic field or aligned against the field. If an external magnetic field is applied, an energy transfer is possible between ground state to excited state. When the spin returns to its ground state level, the absorbed radiofrequency energy is emitted at the same frequency level. The emitted radiofrequency signal that give the NMR spectrum of the concerned nucleus.

6. CONTINUE The emitted radio frequency is directly proportional to the strength of the applied field.

7. QUANTUM NUMBERS AND THEIR RULES IN NMR All nuclei carry a charge and some nuclei spins on the nuclear axis. This spinning of nuclear charge generates a magnetic dipole along the axis. The angular momentum of the spinning charge i.e. spinning nucleus can be describe in terms of Quantum spin number. Spin number “I” can have value of 0,1/2, 1, 3/2 and so on. I=0 denotes no spin .

8. CONT.

9. INSTRUMENTATION OF NMR

10. COMPONENTS OF INSTRUMENT DESCRIPTION Sample holder It should be chemically inert, durable and transparent to rf radiation. It is generally about 8.5 cm long and 0.3 cm in diameter. B. Permanent Magnet Important feature of the magnet is that it should give homogeneous magnetic field. The strength of the field should be very high i.e., at least 20,000 Gauss, because the chemical shifts are proportional to the field strength. It is also important that the magnetic field be constant over long period of time . For this reason adequate temperature control is necessary to maintain the constant physical dimensions of the magnet. C. Magnetic coils There is a relation between the resonance frequency of the nucleus and the strength of the magnetic field in which the sample is placed. This relationship is expressed by equation : υ = Constant X H Where υ = Resonance frequency of Nucleus, H 0 = Strength of magnetic field.

11. D. Sweep Generator To produce the equal amount of magnetic field pass through the sample. E, Radio Frequency Transmitter A radio transmitter coil that produces a short powerful pulse of radio waves. F. Radio Frequency Receiver A radio receiver coil that detects radio frequencies emitted as nuclei relax to a lower energy level. G. Readout system A computer that analyses and record the data.

12. SOLVENT REQUIREMENT IN NMR The sample cannot be obtained in the pure state so in that case it is necessary to dissolve it or extract it from some other medium. Characteristics of a good solvent is given below: It should be chemically inert towards the sample. It should be easily recoverable if the original sample is required after examination. Solvents containing no hydrogen in the molecule. Examples of solvent used in NMR: Carbon tetrachloride( CCl4) , carbon disulfide( CS 2) , Deuteriochloroform ( CDCl 3 HexadeuterioBenzene ( C 6 D 6 , Deuterium oxide (D 2 O) Note: The deuterium nucleus does not respond, in the same region as the hydrogen nucleus . Substitution of D to H provides elimination of unwanted H signals.

13. RELAXATION PROCESS:

14. CHEMICAL SHIFT The shifts in the position of NMR signal (Compared with a standard reference) resulting from the shielding and deshielding by electrons are referred as chemical shift.