The document provides information about Nuclear Magnetic Resonance (NMR) Spectroscopy, including: 1. A brief history of NMR and important contributors such as Felix Bloch, Edward Purcell, Kurt Wuthrich, and Richard Ernst. 2. Applications of NMR including chemical structure analysis, material characterization, study of dynamic processes, and biomolecular structure determination. 3. Explanations of key NMR concepts such as nuclear spin, precession, resonance frequency, and chemical shift.

1. Nuclear Magnetic Resonance
(NMR) Spectroscopy
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2. Felix Bloch
1905-1983
Edward M. Purcell
1912-1997
Kurt Wuthrich
1938-
Richard R. Ernst
1933-
CW NMR 40MHz
1960
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4. A. Chemical-related research:
1. Analytical tool.
2. Structural characterization of chemical compounds.
B. Material-related research
1. Polymer characterization.
2. C60 (Fullerene).
3. High temperature superconductor research.
4. Heterogeneous catalysis (Ziolite).
5. Surface physics.
C. Study of dynamic processes
1. Reaction kinetics.
2. Study of equilibrium (chemical or structural).
D. Structural (three-dimensional) studies
1. Proteins.
2. DNA/RNA. Protein complexes with DNA/RNA.
3. Polysaccharides
Why bother learning NMR?
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5. E. Drug design
1. Structure Activity Relationships (SAR) by NMR
F. Biomedical applications:
1. Metabolic studies of biological systems.
2. Magnetic Resonance Imaging (MRI), diagnostic
imaging, flow imaging, chemical shift imaging, functional
imaging.
3. Macromolecular structure determination in solution.
Finally, it’s the biggest, meanest, most expensive piece of
equipment you’ll see in your career, and this is a great time to
get your hands on it...
Why bother learning NMR?
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6. Nuclear Spin explanation
• The spinning charged nucleus generates a
magnetic field.
=>
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7. Protons (and other nucleons) have Spin
Spin up (+1/2) Spin down (-1/2)
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8. Each Spinning Proton is Like a “Mini-
Magnet”
Spin up Spin down
N
S
N
S
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9. The nucleus in free state
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10. Nuclear spins
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11. Principles of NMR
 The nucleus spin on its own axis and magnetic moment is created,
resulting in the precessional orbit with a frequency called as
processional frequency.
 The nucleus of hydrogen atom behaves as spin bar magnet because
it possess both electric and magnetic field.
 NMR involves the interaction between an oscillating magnetic field
of EMR and the magnetic energy of the hydrogen nucleus or some
other nuclei, when they are placed in external magnetic field.
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12. In any magnetic field, magnetic nuclei like proton precess at a
frequency, v which is proportional to the strength of the applied field.
The exact frequency is expressed by
v=µN Bo/hI
Where Bo =strength of the external field experienced by the proton
I=Spin quantum number
h=Planks constant (6.626x10-34 Js)
µ=Magnetic moment of the particular nucleus
N= Nuclear magnet on constant
L=angular momentum associated with the nuclei
We can think of nuclei as small magnetized tops that spin on their axis:
• The magnetic nuclei has two forces acting on the spins.
•One that tries to turn them towards Bo, and the
other that wants to maintain their angular momentum.
The net result is that the nuclei spins like a top
Bo
wo
m
L
m
L
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Precessional Frequency or Larmor frequency

13. Precession (continued)
•Spins won’t align with Bo, no matter what their intiial orientation was. Spins
pointing ‘up’ and ‘down’ don’t exist!
• Spins will precess at the angle they were when we turned on
the magnetic field Bo:
Bo
There are several magnetic fields acting on the spins. One is Bo, which is
constant in time and generates the precession at wo. The others are fluctuating
due to the molecular anisotropy and its environment, and make the spins ‘try’ all
the possible orientations with respect to Bo in a certain ammount of time.
Orientations in favor of Bo will have lower magnetic energy, and will be slightly
favored.
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14. Principles of NMR
 All nuclei in a molecule are surrounded by electron clouds
H effective=H applied - H local
 The local magnetic field can either reinforce the applied
magnetic field, deshield the hydrogen nucleus, and hence a
higher frequency will be required to bring it into resonance.
 The local magnetic field can oppose the applied magnetic field,
shield the hydrogen nucleus from the strength of the magnetic
field and hence a lower frequency will be required to bring it
into resonance.
 Thus slightly different amounts of energy are needed to excite
each individual hydrogen nucleus to its own higher energy
level.
 In summary, different electron densities create different
magnetic environments around each hydrogen atom and
therefore a series of signals are seen across a spectrum.
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15.  A nucleus with an odd atomic number or an odd mass number has
a nuclear spin.
 The angular momentum of the charge is described as spin number.
They have 0, ½,1, 3/2…etc (I =0 denotes no spin)
 Each proton and neutron has its own spin. If sum of the proton
and neutron is even, spin number (I)= 0,1,2,3, etc
 If sum of the proton and neutron is odd I is half integral=1/2, 3/2,
5/2…etc
Principles of NMR
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16.  All nuclei carry a charge and in
some nuclei this charge spins around
an axis generating a magnetic dipole
along the axis of the nucleus.
 1H has a spin I = ½. There are two
allowed spin states –½ and +½. In
the absence of a magnetic field the
two spin states are degenerate and
are equally populated.
 In a magentic field the low energy
spin state is aligned with the
magnetic field and the high energy
opposed to it.
Principles of NMR
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17. The case of 1/2 spin nuclei. Presence of external field orients the spins.
Spins that are opposed to the field have higher energy than spins that are
aligned with the field.
Principles of NMR
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18. NMR equation
• Energy difference is proportional to the magnetic field
strength.
• E = h =  h B0
2
• Gyromagnetic ratio, , is a constant for each nucleus
(26,753 s-1gauss-1 for H).
• In a 14,092 gauss field, a 60 MHz photon is required to
flip a proton.
• Low energy, radio frequency.
• =>
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19.  The sample absorb different EMR at different frequency.
The spinning axis of the top moves slowly around the
vertical.
 It has been found that the proton precesses about the axis
of the external magnetic field
It has been found that w =  Ho --------(1)
 Where w= angular precessional velocity
Ho =applied field in gauss
 = Gyromagnetic ratio = 2m
hI
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20. Here m=magnetic movement of the spinning bar magnet
I = is the spin quantum number of the spinning magnet
h= Planck’s constant
According to the fundamental NMR equation which
correlates EMR frequencies with the magnetic field we
say that
 Ho =2m ------------(2)
Here v is the frequency of EMR
From equation 1) and 2)
Angular precessional velocity w = 2v
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21.  Precessional frequency is defined as the number of
revolution per second made by the magnetic movement
vector of the nucleus around the external field Ho
 Alternatively the precessional frequency of the spinning
bar magnet (nucleus) may be defined as equal to the
frequency of EMR in megacycles per second necessary to
induce transition from one spin state to another.
 All nuclei carry a charge , so they will possess spin
angular- momentum. The nuclei which have a finite value of
spin quantum number (I >0) will precess along the axis of
rotation.
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22. Nuclear spin is the total nuclear angular momentum quantum number.
This is characterized by a quantum number I, which may be
integral, half-integral or 0.
 Only nuclei with spin number I  0 can absorb/emit
electromagnetic radiation. The magnetic quantum number mI has
values of –I, -I+1, …..+I ( e.g. for I=3/2, mI=-3/2, -1/2, 1/2, 3/2 ).
 1. A nucleus with an even mass A and even charge Z  nuclear
spin I is zero. Example: 12C, 16O, 32S  No NMR signal
2. A nucleus with an even mass A and odd charge Z  integer
value I. Example: 2H, 10B, 14N  NMR detectable
3. A nucleus with odd mass A  I=n/2, where n is an odd
integer. Example: 1H, 13C, 15N, 31P  NMR detectable
Properties of the Nucleus
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23.  If the oriented nuclei are now irradiated with EMR of
proper energy, frequency absorption occurs and the lower
energy spin flips to higher energy state.
 When this spin flip occurs, the nuclei are said to be in
Resonance with applied radiation, hence named NMR.
 The exact amount of RF energy necessary for resonance
depends on the strength of external magnetic field and the
nuclei being irradiated.
Strong magnetic field higher energy
Weaker magnetic field less energy
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C
C

26. Magnetic Shielding
• If all protons absorbed the same amount of energy in
a given magnetic field, not much information could be
obtained.
• But protons are surrounded by electrons that shield
them from the external field.
• Circulating electrons create an induced magnetic field
that opposes the external magnetic field.
=>
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27. Shielded Protons
Magnetic field strength must be increased for a
shielded proton to flip at the same frequency.
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28. Protons in a Molecule
Depending on their chemical environment,
protons in a molecule are shielded by
different amounts.
=>
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29. Different Isotopes Absorb at Different
Frequencies
low frequency high frequency
2H 15N 13C 19F 1H
30 MHz 50 MHz 125 MHz 480 MHz 500 MHz
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30. The chemical shift
The resonant frequency of a certain atom is called chemical
shift.
Advantages:
More compact annotations
Independent on the spectrometer field
In practice, the 1H chemical shifts are in the range 0-10 ppm
The chemical shift depends on:
The atom type (NH, aliphatic CH, aromatic CH, ...)
The amino acid type (Ala, Phe, ...)
The chemical (spatial) environment
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31. NMR Signals
1. The number of signals shows how many different kinds
of protons are present.
2. The location of the signals shows how shielded or
deshielded the proton is.
3. The intensity of the signal shows the number of
protons of that type.
4. Signal splitting shows the number of protons on
adjacent atoms.
5. To define the position of absorption the NMR chart is
calibrated by using TMS highly shielded molecule. The
exact place on the chart at which a nucleus absorb is
called “chemical shift”
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32. Chemical shift of TMS is arbitrarily set the zero point
1= 1ppm of the spectrometer operating frequency
1H NMR, 60MHz operating instrument 60,000,000
1= 1ppm (or) 60Hz
100MHZ operating instrument 1= 100Hz
 (ppm)= observed chemical shift (no.of Hz away from TMS)
Spectrometer frequency in MHz
If the induced field, opposes the applied field the electrons
are diamagnetic& the effect is diamagnetic shielding.
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33. The Chemical Shift of Different Protons
a) NMR is of no use if all protons absorbed at same frequency.
b) What makes it useful is that different protons usually appear at different
chemical shifts.
c) So, we can distinguish one kind of proton from another.
d) Why do different protons appear at different place?
e) Shielding- if there is more electron density around a proton, the signal
appear in high field
f) If less electron density means the signal appear in down field.
C H
Z
This represents the electron density of a C-H bond. How much electron
density is on the proton depends on what else is attached to the carbon. If Z
is an elelctronegative atom, the carbon becomes electron deficient and pulls
some of the electron density away from the H. if Z is an electron donating
group, more electron density ends up on the H.
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34. The Chemical Shift of Different Protons
How do the electrons shield the magnetic field?
By moving. A moving charge creates a magnetic field, and the
field created by the moving electrons opposes the magnetic
field of our NMR machine.
It’s not a huge effect, but it’s enough to enable us to distinguish
between different protons in our sample.
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35. Types of NMR
 Continuous wave (cw) NMR
It detects the resonance of nuclei
 FT NMR
Directly recording the intensity of absorption as a function of
frequency
 The magnet used in NMR produces strong magnetic field
sample probe
1) Sample probe contained between the poles of the magnet
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36. 1. The probe has another coil wrapped at right angles to the
transmitter coil
2. Thus the optimum angle for detecting resonance
3. Various temp probe helps to keep the sample at different
temp (-100 to 200°C)
4. So NMR can be used for kinetic study, thermodynamics
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37. 12/15/2019
The chemical shift (δ) is defined as the difference between
the resonance position of a nucleus and that of a standard
reference compound.
Chemical shift (δ) =[Δν (Hz)/Applied resonance
frequency × 106 Hz)] × 106 ppm
where, Δν = Difference in frequency (Hz) between
the observed signal and that of the standard.
Convention for δ : TMS assigned (δ = 0), values
for other protons are measured positively downfield.
In other words, increasing δ corresponds to
increasing de-shielding of the nucleus.

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Spin-spin Interactions
High resolution NMR spectra very often exhibit
signals as multiplets, invariably showing a more or
less symmetrical appearance.
Multiplicity is brought about due to the splitting of
the signal of one set of equivalent nuclei by the
magnetic fields of adjacent sets of nuclei i.e.,
spin-spin interactions.

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Block Diagram of NMR Spectrometer

40. Radiofrequency Oscillator
• It generated by electronic multiplication and natural
frequency of quartz crystal contained in a thermostated
block/different crystal/trasmitters are used
• RFO installed perpendicular to the magnetic field &
transmits RW of fixed frequency 60,100, 200 or 300 MHZ
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41. RF receiver/detector:
a) The sample in the NMR probe gives data which can be
detected as a signal
b) Detectors used in NMR should be sensitive as the
signal levels are small(<1milli volt)
c) So that multiplication of signal is essential
d) Rf receiver also to be perpendicular to the magnet like
oscillator
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42. Recorder
 The signal is sent to the recorder or oscilloscope
 It helps fast scanning of spectrum or electronic filtering of
signal
 The recorder plots resonance signal on y-axis and strength
of magnetic field on x-axis
 The strength of resonance signal  number of nuclei
resonating at that field strength
 Most spectrometer equipped with automatic integrator to
measure the area under the observed signal
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43. Solvents
CDCl3
• Advantages for non-polar to polar compounds
• CDCl3 peak appear in 7.27δ for sparingly soluble
compounds add drop wise (DMSO-d6)
• It will shift residual CHCl3 peak to 8.38δ
CCl4 for non polar compounds any water molecule causes
turbidity
DMSO-d6
• More viscous/restricted rotation, causes line broadening
non-volatile (difficult to remove from the sample)
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44. Additional Factors Affecting
Chemical Shift
 It is very difficult to predict the chemical shift of protons
attached to heteroatoms (O-H, N-H, S-H).
 It is due to hydrogen bonding which has the effect
deshielding the proton and it causes broadening of
signal.
 Replaces the exchangeable protons with deuteriums
which cannot be detected in the proton NMR.
 Hence its chemical shift can be identified without any
problem (It is a useful technique for -OH, NH2 and
COOH
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45. Solvent effect
 Changing the solvent has a dramatic, yet
unpredictable effect on the chemical shift of
signals.
 This is useful if important peaks overlap in a CDCl3
spectrum then another solvent, D6 benzene, D3
acetonitrile etc can be used
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46. Chemical Shift Data
Different kinds of protons typically come at different chemical shifts.
Shown below is a chart of where some common kinds of protons appear in
the delda scale.
Note that most protons appear between 0 and 10 ppm. The reference,
tetramethylsilane (TMS) appears at 0 ppm, and aldehydes appear near 10
ppm.
ppm
TMS
CH3CH3
RONR2
CH3OCH3
RO
HR
R R
HH
RO
Ph CH3
HR
Cl
CH3
Ph
OH
OH
R
NH
R
Upfieldregion
of the spectrum
Downfieldregion
of the spectrum
TMS = Me Si
Me
Me
Me
012345678910
CH3HO
(R)
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47. Applications
• Determination of exact structure of drugs
and drug metabolites - MOST POWERFUL
METHOD KNOWN
• Detection/quantitation of impurities
• Analysis/deconvolution of liquid mixtures
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48.  Analysis of blood, urine and other biofluid
mixtures to quantify and identify metabolite
changes
 Allows one to detect drug toxicity and even
localize toxicity (for preclinical trials) in a non-
invasive way
 Detection, identification and quantitation of
primary and secondary drug metabolites
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49. Other Applications
• Clinical testing (detection of inborn errors of
metabolism, cancer, diabetes, organic solvent
poisoning, drugs of abuse, etc. etc.)
• Cholesterol and lipoprotein testing
• Chemical Shift Imaging (MRI + MRS)
• Pharmaceutical Biotechnology (proteins,
protein drugs, SAR by NMR)
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50. Hydrogen and Carbon Chemical Shifts
=>
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51. Acknowledgement
•http://www.pharmacy.ualberta.ca/pharm325
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