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To be successful in using NMR as an analytical tool, it is
necessary to understand the physical principles on which the
methods are based.
Key Words;
1. Spin?
2. Charge particle
3. Magnetic Field rules.
4. Shieleded & De-shielded
5. Chemical Shift;
6. Reference Standard Molecule (TMS).
7. Electronegative charge
8. spin-Spin Interaction
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An Electric Charge Momentum
All part of an ATOM ( proton, neutron and electron),
are SPINNING around their own axis.
Around their Axis
A kind of momentum.
5. Magnetic fields shields charge particles.
Inter-action among magnetic fields are neutralized each
other.
In an ATOM;
If One non-neutralized Magnetic Field has been left
This ATOM has 1 from 2 SPIN .
(SPIN ½)
6. Theoretically,
those atom with an Odd atomic number possess a SPIN
1/2.
such as;
• Hydrogen, 1H is the interested atom in H-NMR
spectroscopy.
• Carbon, 13C is the interested atom in C-NMR
spectroscopy.
• Nitrogen, 15N is the interested atom in N-NMR
spectroscopy.
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If Our sample are immersed in a static magnetic field (B 0 ) and then exposed to a
second oscillating magnetic field (B 1), The SPIN will be excited.
When this strong RF signal is switched off, the spins return to their lower state of
energy, producing a small amount of radiation. It induces a radio frequency signal
in a detector coil which is amplified to display the NMR signal.
http://www.agilent.com/labs/images/figure2.jpg
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In (H-NMR) Spectroscopy the nearby protons will experience 3 fields:
1. The static magnetic field (B 0 ). Unifying
2. An oscillating magnetic field (B 1). Disturbing
3. The other magnetic fields in neighbors (shielding field). (Different
resonances.)
http://www.agilent.com/labs/images/figure2.jpg
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An standard Molecule is added to the sample to produce a Reference signal in the
spectrum of NMR.
A Reference standard Molecule should be;
1. Chemically unreactive,
2. Easily removed from the sample after the measurement.
3. Giving a single sharp NMR signal that does not interfere with other resonances.
Tetramethylsilane, (CH3)4Si, usually referred to as TMS, meets all these characteristics.
and has become the reference compound of choice for
0
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0
The resonant frequency signal of the
Reference (TMS)considered as 0
The Chemical Shift, having units of parts-per-million (ppm) δ
TMS consists of 12 equivalent proton and 4
equivalent carbon by symmetry.
Hydrogen of other molecules in our sample are
compared with hydrogen of TMS in terms of
symmetry.
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10 9 8 7 6 5 4 3 2 1 0
Proton Chemical Shift Ranges. ppm(δ)
.
Two major factors that influence proton shielding
An electronegative atoms near the proton can De-shielded Proton´s
magnetic field
proton Spin- spin inter-action, The Magnetic anisotropy means that there
is a "non-uniform magnetic field". It means that; the more hydrogen bonding there is,
the more the proton is De-shielded and the higher its chemical shift will be.
ShieldedDe-shielded
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10 9 8 7 6 5 4 3 2 1 0
Proton Chemical Shift ppm(δ)
Proportionaltothemolarconcentrationofthesample.
AND a six-membered Ring, generally display a very low-field proton
resonance
Electronegative groups attached to the C-H system
decrease proton´s shielding (i.e.de-shielding)
so increases the chemical shift.
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The number of splitting indicates the number of Proton in the vicinity of the Proton, in the
strong position.
No Coupling One Coupling
Coupling constant
J
The size of the splitting (coupling constant or J) is independent of the magnetic field
Three Coupling
Coupling constant
J
Two Coupling
Coupling constant
J
Coupling arises because the magnetic field of
vicinal (adjacent) protons
16. Bringing together:
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4. TMS is a Reference Standard Molecule in Proton and Carbon NMR
spectroscopy
1. An electrical charge which moves (spins) set up a magnetic field.
2. Rotation a charged particle around their own axis is called spin!
3. Inter-action between a charged spinning particle field and en
external field can be measured by NMR Spectroscopy.
5. TMS cconsists of symmetrical protons and carbons.
6. Chemical shift is an scale which symmetry of protons’ spin compare
with TMS’.
At the END
Thanks for your Attention.
