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NMR spectroscopy is the study of spin changes at the
nuclear level when a radiofrequency energy is absorbed
in the presence of magnetic field.
The energy required for NMR lies in the low
energy or long wavelength radio frequency.
Magnetic field is applied
Any proton or nucleus with odd
Its spin on its own axis and magnetic
moment is created with a frequency
called as precessional frequency
This state is called ground state or parallel
In this state magnetic field caused by spin of
nuclei is aligned with externally applied
Radiofrequency is applied (energy)
Absorption of energy, nucleus move
from G.S to E.S
Results- spin reversal anti-parallel orientation
Application of radiofrequency is stopped
Nucleus returns to G.S or parallel orientation
Theory of FT-NMRTheory of FT-NMR
Magnetic nuclei in magnetic field
Pulse of radio frequency is irradiated
Nuclei absorb some of the energy
Precess (spin) like little tops
(signal) Free induction decay (FID)
is converted to spectrum
A complex signal is produced, then
decay as nuclei lose energy
• FT-NMR is more sensitive and can
measure more weaker signals.
• Dramatic increase in the sensitivity of
• Can be obtained with less than 5mg of
• The signal stand out clearly with almost
no electronic background noise
• Used in engineering, industrial quality
control and medicine.
• The FT-NMR method also gives
improved spectra for sparingly soluble
• Text book of pharmaceutical analysis by
Ravisankar, page no: 6-2 to 6-4
• https://www.bijayauprety-nmr 41214142