NMR
Spectroscopy
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
A spinning charge generates a magnetic field , as shown by the
animation

The resulting spin magnet has a magnetic moment (µ ) proportional
to magnetic spin .
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
When a spin-active hydrogen atom is placed in a strong magnetic
field , it begins to precess
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The parallel and
anti-parallel
position of
nucleus depends
on concerning
external magnet .
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Energy
difference
increases with
increasing
magnetic field
Nuclei in Magnetic Field

Distribution between two states
N+½
/ N-½ = e
ΔE/k T
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Larmor Motion

It is the frequency at which the hydrogen precess
When hydrogen is near an externally applied magnetic field, an
increase or decrease causes the precessional frequency or
resonant frequency also increase or decrease.

Larmor frequency , ν∝B0
ν=(γ/2π)B0


The constant γ is called the gyromagnetic ratio

Gyromagnetic ratio increases with increasing strength of magnet

Angular frequency , ω =γB0

ΔE = hν = h(γ/2π)B0
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Diamagnetic Anisotropy
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NMR Instrumentation
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Chemical Shift
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
Chemical shift δ is usually expressed in parts par million (ppm)
by frequency, because it is calculated from

Chemical shift = δ = νsample -νref
ν0
*106
This division gives a number independent of the instrument used .
TMS( Tetra-methyl
silene)

TMS is the most shielded compound. It is
a volatile compound . By giving heat, we
can remove the TMS from a compound.
It will not give any disturbance .
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Even mass nuclei composed of even number of
neutrons and protons have I=0 ( not interesting
from the NMR point of view). Examples are12C ,16O
Active Nuclei
in NMR
Even mass nuclei composed of odd number of
neutrons and protons have an integer spin
quantum number . Examples are I=1 (2H,14N)
Odd mass nuclei have half integer (fractional) spin
quantum number. Examples are I=½(1H ,
13C,19F),I=3/2(11B)
Applications Of NMR

It is an analytical chemistry technique used
in quality control.

It is used in research for determining the content
and purity of a sample as well as its molecular
structure. For example, NMR can quantitatively
analyze mixtures containing known compounds.

NMR spectroscopy is routinely used by chemists
to study chemical structure using simple onedimensional techniques. Two-dimensional
techniques are used to determine the structure
of more complicated molecules.
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Applications of NMR

These techniques are replacing xray crystallography for the determination
of protein structure .

Time domain NMR spectroscopy techniques
are used to probe molecular dynamics
in solution.

Solid state NMR spectroscopy is used to
determine the molecular structure of solids
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Applications of NMR

Most people are familiar with Magnetic
Resonance Imaging (MRI) scans which use
powerful magnetic fields and radio waves to
reveal detailed images of the internal organs.
Data is generated based on rates of
absorption and energy emission recorded in
the radiofrequency (RF) range. The medical
imaging technique is founded in NMR
Spectroscopy and uses the same basic
principles.
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