Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy or magnetic resonance spectroscopy, is a spectroscopic technique to observe local magnetic fields around atomic nuclei.

1. NUCLEAR
MAGNETIC
RESONANCE
(NMR)

2. PRESENTED BY
Maham Adnan

3. INTRODUCTION
Nuclear magnetic resonance (NMR)
spectroscopy is a widely used analytical
technique for organic compounds.
It is a spectroscopy technique which is based
on the absorption of electromagnetic radiation
in the radio frequency region 4 to 900 MHz by
nuclei of the atoms.
NMR is based on the fact that the nucleus of
each hydrogen atom in an organic molecule
behaves like a tiny magnet.
The spinning motion of the positively charged
proton causes a very small magnetic field to be
set up.
Spin of Hydrogen Atom

4. NMR is the most valuable spectroscopic
technique used for structure determination.
More advanced NMR techniques are used in
biological chemistry to study protein structure
and folding NMR Spectroscopy.
Spectroscopy determines the physical and
chemical properties of atoms or the molecules
in which they are contained and provide
detailed information about the structure,
dynamics, reaction state, and chemical
environment of molecules.
It is used to study a wide variety of nuclei:
– 1H
– 15N
– 13C
– 31P

5. HISTORY
Nuclear magnetic resonance was first described
and measured in molecular beams by Isidor Rabi
in 1938. Rabi was awarded the Nobel Prize in
Physics for this work.
In 1946, Felix Bloch and Edward Mills Purcell
expanded the technique for use on liquids and
solids, for which they shared the Nobel Prize in
Physics in 1952.
Russell H. Varian filed the "Method and means
for correlating nuclear properties of atoms and
magnetic fields", U.S. Patent on July 24, 1951.
Varian Associates developed the first NMR unit
called NMR HR-30 in 1952.
Isidor Isaac Rabi

6. TYPES
Two common types of NMR spectroscopy are used to characterize organic
structure:
– 1 H NMR:- Used to determine the type and number of H atoms in a
molecule
– 13 C NMR:- Used to determine the type of carbon atoms in the molecule

7. SOURCE
The source of energy in NMR is radio waves which have long
wavelengths having more than 107 nm, and thus low energy and
frequency.
When low-energy radio waves interact with a molecule, they can
change the nuclear spins of some elements, including 1 H and 13
C.

8. PRINCIPAL
The principle is based on the- spinning of
nucleus and generating a magnetic field.
Without external magnetic(Bo) – field nuclear
spin are random in direction.
With Bo nuclei align themselves either with or
against field of external magnetic field.
If an external magnetic field is applied, an
energy transfer (ΔE) is possible between
ground state to excited state. When the spin
returns to its ground state level, the absorbed
radiofrequency energy is emitted at the same
frequency level.
The emitted radiofrequency signal that give
the NMR spectrum of the concerned nucleus.

9. THEORY
In NMR we put the sample to be analyzed in a magnetic field. The hydrogen nuclei
(protons) either line up with the field or, by spinning in the opposite direction, line
up against it.
 Some nuclei experience this phenomenon, and others do not, dependent upon
whether they possess a property called spin.
In a magnetic field, there are now two energy states for a proton:
– A lower energy state with the nucleus aligned in the same direction as Bo,
– A higher energy state in which the nucleus aligned against Bo.

10. There is a tiny difference in energy
between the oppositely spinning 1
H nuclei. This difference
corresponds to the energy carried
by waves in the radio wave range
of the electromagnetic radiation
spectrum.
In NMR spectroscopy the nuclei
‘flip’ between the two energy
levels.
Only atoms whose mass number is
an odd number, e.g. 1H or 13C,
absorb energy in the range of
frequencies that are analyzed.
The energy difference between

11. TETRAMETHYLSILANE (TMS)
As the magnetic field is varied, the 1H nuclei in
different molecular environments flip at different
field strengths.
The different field strengths are measured relative
to a reference compound, which is given a value of
zero.
The standard compound chosen is
tetramethylsilane (TMS).
TMS is an inert, volatile liquid that mixes well with
most organic compounds.
Its formula is Si (CH3)4, so all its H atoms are
equivalent.
TMS only gives one, sharp absorption, called a
peak, and this peak is at a higher frequency than

12. CHEMICAL SHIFT (Δ)
All other absorptions are measured by their shift away from the TMS line on the NMR
spectrum. This is called the chemical shift (δ), and is measured in units of parts per
million (ppm).
 The relative energy of resonance of a particular nucleus resulting from its local
environment is called chemical shift.
NMR spectra show applied field strength increasing from left to right. Left part is
downfield, the right is upfield.
Nuclei that absorb on upfield side are strongly shielded where nuclei that absorb on
downfield side is weakly shielded.

13. INSTRUMENTATION
The experimental
apparatus consists of four
major systems:
1. A Large Electromagnet,
2. A Transmitting Circuit,
3. A Receiving Circuit,
4. A Computer which
performs analysis on the
received signal.

14. SAMPLE TUBE
Glass tube
with 8.5
cm long,
0.3 cm in
diameter.

15. MAGNET
1. Permanent
Constant Bo is generated that is
0.7;1.4;2.1
Advantages:-
1. Construction is simple
2. Cheaper
2. Electromagnet
Bo can be varied which is done by
winding the electromagnetic coil
around the magnet.
It is the most expensive components of
the nuclear magnetic resonance
spectrometer system

16. SHIM COIL
The purpose of shim coils on a spectrometer is to correct minor
spatial inhomogeneities in the Bo magnetic field.
These inhomogeneities could be caused by the magnet design,
materials in the probe, variations in the thickness of the sample tube,
sample permeability.
 A shim coil is designed to create a small magnetic field which will
oppose and cancel out an inhomogeneity in the Bo magnetic field.

17. SUPERCONDUCTING SOLENOIDS
Prepared from superconducting niobium-titanium wire and niobium-tin wire
Operated at lower temp.
Kept in liquid He(mostly preferred) or liquid N2 at temp of 4 K
Liquid N2 should be changed at 10 days while liquid He shouldd be changed at
80-130 days
Higher Bo can be produced that is upto 21 T.
Advantage:-
1. High stability
2. Low operating cost
3. High sensitivity
4. Small size compared to electromagnets
5. Simple

18. RADIOFREQUNCY TRANSMITTER
It is a 60 MHz crystal controlled oscillator.
RF signal is fed into a pair of coils mounted at right angles to the path
of field.
The coil that transmit RF field is made into 2 halves in order to allow
insertion of sample holder .
2 halves are placed in magnetic gap
For high resolution the transmitted frequency must be highly constant.
The basic oscillator is crystal controlled followed by a buffer doubler,
the frequency being doubled by tuning the variable
It is further connected to another buffer doubler tuned to 60 MHz
Then buffer amplifier is provided to avoid circuit loading.

19. SIGNAL AMPLIFIER AND DETECTOR & THE
DISPLAY SYSTEM
Signal amplifier and detector
Radiofrequency signal is produced by the resonating nuclei is detected
by means of a coil that surrounds the sample holder
The signal results from the absorption of energy from the receiver coil,
when nuclear transitions are induced and the voltage across receiver coil
drops
This voltage change is very small and it must be amplified before it can
be displayed.
The display system
The detected signal is applied to vertical plates of an oscilloscope to
produce NMR spectrum
Spectrum can also be recorded on a chart recorder.

21. SAMPLE PROBE
The sample probe is the name given to that part of the spectrometer which accepts
the sample, sends RF energy into the sample, and detects the signal emanating
from the sample.
It contains the RF coil, sample spinner, temperature controlling circuitry, and
gradient coils.
It is also provided with an air driven turbine for rotating the sample tube at several
hundred rpm
This rotation averages out the effects of in homogeneities in the field and provide
better resolution.
The spectrum obtained at constant magnetic field is shown in series of peaks
whose areas are proportional to the number of protons they represent.
Peak areas are measured by an electronic integrator that traces a series of steps
with heights proportional to the peak areas.

22. THE CONTINUOUS-WAVE (CW)
INSTRUMENT

23. WORKING
The sample is dissolved in a solvent containing no interfering proton (usually
CCl4 and CDCl3), and a small amount of TMS is added to serve as an internal
reference.
The sample is a small cylindrical glass tube that is suspended in the gap
between the faces of the pole pieces of the magnet.
The sample is spun around the axis to ensure that all parts of the solution
experience a relatively uniform magnetic field.
Also in a magnetic gap is a coil attached to 60-MHz radiofrequency
generator. This coil supplies the electromagnetic energy used to change the
spin orientation of the protons.
Perpendicular to the RF oscillator coil is a detector coil. When no absorption
of energy is taking place, the detector coil picks up non of the energy given
off by the RF oscillator coil.

24. When sample absorbs energy, however, the reorientation of the
nuclear spins induces a radiofrequency signal in the plane of the
detector coil, and the instrument responds by recording this as a
resonance signal, or peak.
Rather than changing the frequency of the RF oscillator to allow each
of the protons in a molecule to come into a resonance, the typical
NMR spectrometer uses a constant frequency RF- signal and varies
the magnetic field strength.
As the magnetic field strength is increased, the precessional
frequency of all the protons increase. When the precesional
frequency of a given type proton reaches 60MHz, it has resonance.

25. As the field strength is increased linearly, a pen travels
across a recording chart.
A typical spectrum is recorded as shown in fig below.

26. As each chemically distinct type of
proton comes into resonance, it is
recorded as a peak on the chart.
The peak at δ = 0 ppm is due to
the internal reference compound
TMS.
IN THE CLASSICAL NMR
EXPERIMENT THE INSTRUMENT
SCANS FROM “LOW FIELD” TO
“HIGH FIELD”

27. Since highly shield proton precess more slowly than unshield proton, it
is necessary to increase field to induce them to precess at 60MHz and
hence highly shield proton appear to the right of this chart and
deshield proton appear to the left.
Instruments which vary the magnetic field in continuous fashion,
scanning from downfield to upfield end of the spectrum, are called
continuous-wave(CW) instrument.
Because the chemical shift of the peak in this spectrum are calculated
from frequency difference from TMS, this type of spectrum is said to be
a frequency-domain spectrum.
Peaks generated by a CW instrument have ringing. Ringing occurs
because the excited nuclei do not have time to relax back to their
equilibrium state before the field. And pen, of the instrument have
advanced to a new position.
Ringing is most noticeable when a peak is a sharp Singlet.

28. APPLICATIONS OF NMR
1. Medicine
2. Chemistry
3. Purity determination
4. Non destructive testing
5. Data acquisition
6. Magnetomers
7. SMNR

29. 1. MEDICINE
 Magnetic resonance imaging (MRI)
is best known for medical diagnosis.
 it is widely used in NMR
spectroscopy such as proton NMR,
carbon-13 NMR, deuterium NMR
phosphorus-31 NMR.
 Biochemical information can also be
obtained from living tissue with the
technique known as chemical shift
NMR microscopy.
 NMR is used to generate metabolic
fingerprints from biological fluids to
obtain information about disease
states or toxic insults.

30. 2. CHEMISTRY
 By studying the peaks of
nuclear magnetic resonance
spectra, the structure of many
compounds can be
The identification of a
compound by comparing the
observed nuclear precession
frequencies to known
frequencies. Further structural
data can be elucidated by
observing spin-spin coupling.

31. 3. Non- destructive
testing
Nuclear magnetic
resonance is extremely
useful for analyzing
samples non-
destructively.
For example, various
expensive biological
samples, such as nucleic
acids, including RNA
and DNA, or proteins

32. 4. PURITY DETERMINATION
 NMR can also be used for purity determination.
This technique requires the use of an internal standard
known purity.
 the purity of the sample is determined via the following
equation.

33. 5. DATA ACQUISITION
Another use for nuclear
magnetic resonance is data
acquisition in the petroleum
industry for petroleum and
natural gas exploration and
recovery.
Initial research in this domain
began in the 1950s
 It is possible to infer or
estimate:
 The volume (porosity) and
distribution (permeability) of
the rock pore space
 Rock composition
 Type and quantity of fluid
hydrocarbons

34. 6. Magnetomers
Various magnetometers use NMR effects to measure
fields
 Including proton precession magnetometers (PPM)
7. Surface Nuclear Magnetic Resonance (SNMR)
Surface magnetic resonance can be used to indirectly
the water content of saturated and unsaturated zones in the
earth's subsurface.
SNMR is used to estimate aquifer properties, including
of water contained in the aquifer, Porosity and Hydraulic
conductivity.

35. ADVANTAGES AND DISADVANTAGES
Advantages
1. It is non-destructive.
2. it can be used for large variety of molecules.
3. It can be used for both solid and liquid phases.
4. it can be operate for a variety of temperatures (from 77K to over
350K).
Disadvantages
1. it is expensive method.
2. time consuming.
3. the resolving power of NMR is less than other type of experiment
e.g. X-ray crystallography

36. SOLVENTS IN NMR
Properties
1. Nonviscous.
2. Should dissolve analyte.
3. Should not absorb within spectral range of analysis.
4. All solvents used in NMR must be aprotic that is they should not
possess proton.
Solvents
Chloroform-d (CDCl3) is the most common solvent for NMR
measurements
Other deuterium labeled compounds, such as deuterium oxide (D2O),
benzene-d6 (C6D6), acetone-d6 (CD3COCD3) and DMSO-d6
are also available for use as NMR solvents.
DMF, DMSO, cyclopropane, dimethyl ether can also be used

37. THANK YOU !