Nuclear Magnetic Resonance Spectroscopy
Definition of NMR:-
Nuclear magnetic resonance is defined as a condition when the frequency of the rotating magnetic field becomes equal to the frequency of the processing nucleus.
If ratio frequency energy and a, magnetic field are simultaneously applied to the nucleus, a condition as given by the equation v=γH0/2π is met. The system at this condition is said to be in resonance
[v= frequency, γ= proportionalitt constant and H0= magnetic field].
Theory of NMR:-
The hydrogen nucleus or protons can be regarded as a spinning postively charged unit and so it will generate a tiny magnetic field HO along its spinning axis. Now if this nucleus is placed in an external magnetic field HO, it will naturally line up either parallel.
(1) Relaxation Process- Relaxation processes are defined as different types of radiation-less transitions by which a nucleus in an uper spin state returns to a lower spin state.
(2) Condition of Resonance Signals- The atoms loke O16 and C12 which have even number of protons and neutrons have no magnetic momentand here refuse to give resonance signals.
Principle of NMR:-
The principle of nuclear magnetic resonance is based on the spins of atomic nuclei. The magnetic measurements depend upon the spin of unpaired electron whereas nuclear magnetic resonance measures magnetic effect caused by the spin of protons and neutrons.Both these nucleons have intrinsic angular moment or spins and hence act as elementry magnet.
Application of NMR Spectroscopy:-
(1) Quantitative Analysis-
The area of peak is directly propagation to the number of nuclei resopnsible for that peak. Thus the concentration of species can be determined directly by making use of signal area per proton.
(2) Quantitative Analysis-
The qualitative analysis of compound can easily be made by knowing:
a. Chemical shift 8 values of hydrogen containing group
b. The presence of particular function grp.
c. The relative postion of these groups
d. The relative number of nuclei in these group.
Nuclear Magnetic Double Resonance (NIVIDR) -
When two oscillating magnetic field are simultaneously applied to the sample, the experiment is called double resonance,double irradiation, or spin decopling.
Electron Paramagnetic Resonance (EPR)-
The elctron paramagnetic resonance (EPR) differs from NMR principally because in that the frequencies of electron resonance occur in microwave region for magnetic fields of the order of several thousand gauss. Therefore EPR spectrometer used such components as Klystrons,wave guides and resonance cavities for the sample.
EPR method is applicable whenever the compound displays at least one unpaired electron, i.e., in free radicals , crystalline and amorphous solids.
Units of NMR:-
1. δ-the reference compound be quoted.
2. Cps - the reference compound must be quoted and the oscillator frequency given.
3.T-TMS (tetramethylsilane) is assumed independent of both oscillator frequency and reference compund.
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