NMR Spectroscopy jayprakash nogaja

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Meaning of Different Chemical & Magnetic Environment ? What is Spinning of protons ? What is The need of Magnetic Field ? Concepts of 1)Precessional Motion. 2)Precessional Frequency . 3)Gyroscopic Motion. Principle of NMR with therotical explanation , Instrumentation

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Nuclear Magnetic Resonance Spectroscopy (NMR):

1 Nuclear Magnetic Resonance Spectroscopy (NMR) Presented By :- Mr.Jayprakash S.Nogaja M Pharmacy-IIyr (Pharmaceutics) jpnogja@rediffmail.com

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2 ( NMR ) H-NMR / Proton NMR “ NMR is the branch of spectroscopy in which radiofrequency waves induces transitions between magnetic energy levels of nuclei of a molecule .The energy levels are created by keeping the nuclei in a magnetic field .” Measures Magnetic properties of nuclei. Nuclear Magnetic Resonance Spectroscopy

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3 Protons of different chemical environment produces their own unique pick. hence different types of protons in am molecule produce different picks NMR Spectroscopy is based up on the measurement of absorption of electromagnetic waves by the spinning nuclei in the radiofrequency region of range 4 to 900 MHZ (V)

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4 What is meaning of Different Chemical & Magnetic Environment ?

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5 Eg – in Aliphatic compounds

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6

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7 What is meaning of Different Chemical & Magnetic Environment : 5 ring Protons 6 ring Protons 5 ring Protons 3 methy Protons 3 methyl Protons 5 u 3u Reff.std. 6 u Reff.std. Eg – in Aromatic compounds

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8 What is Spinning of protons ? This behaves as Induced Field magnet Nucleus (1 proton,0 neutron ) Positive Center Electron Negative Center The nucleus of hydrogen atom (proton) behaves as a tiny Spinning bar magnet .

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9 What is The need of Magnetic Field ? Aligned /Parallal /attration energy /low energy (E1)/ +1/2 / α Opposed /Antiparallal /Repulsion Energy/ High Energy (E2) /-1/2 / β Ans :To create magnetic energy levels in nuclei of a molecule The transition from one energy state to another is called as Flipping of proton occurs due to absorption of EMR

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10 Induced Magnetic Field in proton-

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11 Now this Aligned or Opposed precessing protons will absorb energy from the radiofrequency sourse only if its precessing frequency is equals to ferquency of beam.when this occures,the nucleus and the radiofrequency beam are said to be in resonance ,hence the term NMR

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12 Radiation source /Energy source : The wave lengths and energy required in NMR spectroscopy are far different from that of UV visible & IR . In NMR radiofrequency waves are used which are long wavelength and therefore have less energy associated with them .These do not affect the nuclei in strong magnetic field . Radiofrequency region of range 4 to 900 MHZ

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13 Concepts of 1)Precessional Motion.2)Precessional Frequency .3)Gyroscopic Motion. Aligned Opposed Δ E low energy (E1 ) High Energy (E2) h γ Consider the behavior of spinning top & its spinning motion The top performs warts like motion in which it spins around its vertical axis under the influence of earts gravitational field.This type motion is called as Precessional Motion the top is said to be precessing around vertical axis and at what rate/frequency/revolutions per second is called as Precessional Frequency

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14 The Precession arises from the interaction of spin with earth’s gravity acting vertically downwards is called as Gyroscopic motion. Only Spinning top will precess ,a static top will merely fall over Each type of magnetic nuclei have their different characteristic Precessional Frequency( V ) , So at Specific frequency of RF Radiation only specific proton absorb radiation.

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15 According to Larmor Precession Theory … “The Precessional Frequency( V ) is Directly proportional to Strength of external magnetic field( H 0) .” ω α γ H 0 H 0 = ω ω = Angular precessional Vlocity γ = Gyromagnetic ratio = 2 πμ / h I μ = magnetic moment of the spinning bar magnet I = Spin quantum number of spinning bar magnet. h = Planck’s constant

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16 According to Fundamental equation of NMR γ H 0 = 2 π V V = Frequency of EMR which is equal to Precessional frequency at resonance “The precessional frequency may be defined as the number of revolutions per second mad by the magnetic moment vector of nucleus around the external field H 0 .Alternately is equal to the frequency of EMR in megacycles per second necessary to induce a transition from one spinning state to another”

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17 All nuclei carry charge ,so they will possess spin angular momentum .But only those nuclei having Spin Quantum number (I) greater than 0 (I > 0 )will possess angular momentum along the axis of rotation. So the atomic nuclei with I > 0 show the NMR Phenomenon The spine quantum is depend on Atomic Mass number (A) & Atomic Number (Z) of atom. Atomic Mass number (A) Atomic Number (Z) Spin Quantum number (I) Odd Odd / Even ½,3/2,5/2 … Even Even 0 Even Odd 1,2,3… So, C-13,F-19, P-31,N-14, N-15,O-17 NMR are available NMR is applicable to any nucleus possessing spin .

Instrumentation :

18 Instrumentation When NMR active nuclei (such as 1H or 13C) placed in a magnetic field,it absorb radiation at a frequency characteristic of the isotope . ie.the resonant frequency. It is complex collection of electronic equipment most of power is converted in to heat and vary little converted in to signal To maintain temperature N 2 (-96 º ) gas is used .

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19 1)Sample holder : Generally made up of Glass tube of about 8.5 Cm long & 0.3 Cm diameter. Sample is in Solution form 2 to 10 % diluted solution. Ideal Properties of Solvents : Solvent should not contain H/Proton Devoid of hydrogen atom Non polar Chemically Inert , no reactive with sample Available in pure form. Dissolve sufficient quantity of solute (up to 10 %) Example :CCl 4 ,CS 2 , CDCl 3 ,F3C-COOH,DMSO,D 2 O Ideal Properties of Sample Holder : Transparent to RF radiation. Chemically inert Durable

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20 2) Permanent magnet / External magnet : The permanent magnet or electro magnet can be used for providing stable & homogenous field . The energy of the absorption and the intensity of the signal are proportional to the strength of the magnetic field so field should be strong & controllable / modulable. Generally Magnet size is 15”in diameter produce 23,500 gause for 100MHz

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21 3)Sweep Generator / Sweep Coil : Sweep coil is used for producing & controlling uniform magnetic field. This can be done by 2 ways : 1 ) Field sweep method – If the applied magnetic field is kept constant and RF radiations are changing ,so that it become to resonance frequency 2 ) Frequency Sweep Method – if the frequency of RF radiation is maintained constant & applied magnetic field is changing to bring resonance. Generally the field sweep method is more in use because it easy to modulate frequency of RF radiation than the magnetic field of large stable magnetic field.

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22 Sweep coil is the pair of coils fixed in the pole faces of the stable magnet the magnetic field produced by the coil is added to field which is in the direction of main field. Magnetic field of coil con be varied by varying current flowing through it. 4 )RF Generator /RF Oscillator – The RF Oscillator coil is installed perpendicular to magnetic field and transmit RF waves

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23 5 ) RF Receiver /Detector – A few turns of wire wound tightly around the sample tube perpendicular to both magnetic field and RF Oscillator. When the precessional frequency is matched with the RF of RF Oscillator the nuclei induce electro magnetic field (emf) in the detector coil This signals are amplified and send to recorder . 6 ) Amplifier & Record & Readout System – The absorption signal received from RF is extremely weak so amplification before readout is necessary.

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24 Reference :- 1 ) Organic Spectroscopy By-WILLIAM KEMP ,3 rd Edition page no :100 to 109. 2 ) Instrumental methods of chemical analysis By- Gurdeep R. Chartwal & Sham K. Anand ,Himalaya Publishing House,2009. Page no-2.185-2.23 3) Pharmceutical analysis ,Vol-2, Instrumental method,7 th edition,topic no25. By Dr.K.R.Mahadic,Dr.H.N.More,Dr.A.V.Kasture,Dr.S.G.Wadodkar, Nirali publication.Page no :-222-233. 4 )Organic Spectroscopy By Y.R.Sharma.Page no-132-165

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25 Thank you

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