The document discusses Nuclear Magnetic Resonance (NMR) spectroscopy, an analytical technique for identifying and quantifying substances based on their nuclear properties. It explains fundamental concepts such as chemical shifts, coupling constants, and the necessary instrumentation for high-resolution NMR, including the role of external magnetic fields. Applications of NMR span various fields, including medical imaging (MRI) and biochemical analysis, highlighting its utility in quality control and research.

2. Assigned By: Miss Shehla
Presented By: Fatima-tu-Zahra
Roll no:1427

3. • The NMR phenomenon
Principle
• Precessional frequency (ν)
• Chemical shift
• Spin-spin interactionsTheory
•Chemical shift (δ)
•Multiplicity of the signal
• Coupling constant
Interpretation of
NMR
• Fourier NMR
• Continuous wave NMR
Instrumentation
• Identification testing
• Assay of drugs
Applications

4. • Defined as a condition when the frequency of the applied
magnetic field becomes equal to the frequency of magnetic field
produced by the nucleus.
• Process whereby energy from an external source is absorbed and
brings about a change or resonance to an ‘excited’ or high energy
state
Nuclear Magnetic
Resonance
• An analytical chemistry technique used in quality control and
research for determining the content and purity of a sample as
well as its molecular structure
• The energy required for NMR lies in the low energy or long
wavelength radio-frequency end of the electromagnetic spectrum.
NMR
spectroscopy

5. The nucleus of the hydrogen
atom, i.e., the proton, just
behaves as if it is a small
spinning bar magnet.
It does so because it evidently
possesses an electrical charge
as well as a mechanical spin.
Consequently, a spinning
charged body will generate a
magnetic field.

7. Parallel
orientation
when proton
is aligned
with the field
at lower
energy state
Unparallel
orientation
when proton
is opposed to
the field
at higher
energy state

8. A gyroscope (from Greek gûros, "circle" and
skopéō, "to look") is a spinning wheel or disc in
which the axis of rotation is free to assume any
orientation.
Precession is a change in the orientation of the
rotational axis of a rotating body.
Torque-induced precession (gyroscopic precession) is
the phenomenon in which the axis of a spinning object
(e.g., a gyroscope) describes a cone in space when an
external torque is applied to it

11. HOW
•Whenever a proton is precessing in the aligned orientation (low
energy) it can absorb energy and pass into the orientation (high
energy) ; and subsequently it can lose this extra energy and
relax back into the aligned state
WHEN
•Interestingly, the precessing proton can only absorb energy from
the radio frequency source if the precessing frequency is exactly
the same as that of the radio frequency beam ; and when this
particular situation arises, the nucleus and the radio frequency
beam are said to be in resonance, thereby justifying the term
‘nuclear magnetic resonance’.
HENCE
•In NMR spectroscopy, the precessing protons of an organic
molecule, after being duly exposed to a powerful external
magnetic field (ranging between 60-400 MHz), are irradiated
with radio frequency energy of the appropriate frequencies,
thereby promoting protons from the low-energy (aligned state)
to the highenergy (opposed state).

12. The Spin Quantum
Number (ms)
describes the angular
momentum of an
electron.
An electron spins around
an axis and has both
angular momentum and
orbital angular
momentum.
Because angular
momentum is a vector,
the Spin Quantum
Number (s) has both a
magnitude (1/2) and
direction (+ or -)
Each orbital can only hold two
electrons. One electron will
have a +1/2 spin and the
other will have a -1/2 spin.

13. Mass Number Atomic Number Spin Quantum no.
odd Odd or even I=1/2
even even 0
even odd I=1,2,3….

14.  The chemical shift in absolute terms is defined by the frequency of the
resonance expressed with reference to a standard compound which
is defined to be at 0 ppm. The scale is made more manageable by
expressing it in parts per million (ppm) and is indepedent of the
spectrometer frequency.
downfield or
deshielded
upfield or
shielded

15. Coupling constant
J is the separation (in Hertz ; Hz = sec–1) between the peaks of regular multiplets. The coupling
constants help in the identification of the coupled nuclei because Jab = Jba : and are therefore,
useful in characterizing the relative orientations of interacting protons.
Equivalent and Non-Equivalent protons
Depends on value of chemical shift
Multiplicity of Absorption signal
Depends on neighboring non-equivalent protons(2nI+1)
Singlet----Doublet----Triplet----Quartet
DEFINITON
Effect of spin of one proton on adjacent magnetically non-equivalent proton that
results in splitting of its absorption signal.

18. •For any system at equilibrium, in the absence of a magnetic field, all the nuclear spin states
are equally populated and hence there is no net polarization due to the nuclear spins.
Therefore, it is necessary to introduce an external magnetic field which leads to preferential
population of the lower energy nuclear spin states.
•The energy differences between the different nuclear spin states are proportional to the
strength of the magnetic field. Therefore, higher magnetic fields lead to greater separation
between the energy levels and greater polarization at equilibrium. The required magnetic
field is usually provided by an external magnet.
•For high resolution NMR spectroscopy the magnetic field homogeneity has to be better than
1 ppb (part per billion) over the volume of interest. The homogeneity requirements are
usually lower for MRI and NMR relaxometry. The homogeneity of the magnetic field created
by the primary magnet is improved by using a set of shims.
•High magnetic fields (1 Tesla to 17 Tesla) are generally preferred for high resolution, high
sensitivity NMR spectroscopic experiments. In general, higher magnetic fields provide higher
signal to noise ratio as well as higher resolution. Most high resolution NMR spectrometers
used by chemists and biologists use superconducting magnets.

19. •The probe in an NMR spectrometer is responsible for coupling the radio
frequency electromagnetic field generated by the RF transmitter to the
sample. It is also responsible for detecting the NMR signal (through
induction) and passing it to the receiver for amplification and
digitization.
•In the earliest NMR spectrometers, the probe consisted of a pair of
orthogonal coils. One coil was coupled to the RF transmitter and was
used to generate a homogeneous RF electromagnetic field over the
sample area of interest. Continuous RF or pulses of coherent RF
radiation were used to create transverse magnetization in the sample.
•The precession of this transverse magnetization would cause induction
in a second coil known as the receiver coil. The receiver coil was
orthogonal to the transmission coil. However, at present, most NMR
spectrometers and MRI instruments use a single coil for both
transmission and reception.

20.  MR electronics consists of a subsystems for
controlling the MR transceiver, magnetic field
gradients, field frequency lock, spinner
speed, temperature of the sample (VT), and
an interface to a computer for receiving
controlling instructions and to transmit the
digitized data.

21.  Magnetic field gradients are controlled by an
independent subsystem. Magnetic field
gradients are generated by passing current
through coils of appropriate geometry. Static
magnetic field gradients are used for
shimming. In addition pulsed magnetic field
gradients can be produced based on the
instructions in the pulse program.

22.  The MR transceiver contains two major subsystems: The
transmitter and the receiver subsystems
 Transmitter subsystem: It consists of the RF synthesizers and
amplifiers. This subsystem is responsible for generating pulse
sequences containing RF pulses of specified frequency,
amplitude, phase, shape and duration at specified times.
Multiple RF synthesizers are required because many MR
experiments require simultaneous application of RF pulses of
different frequencies.
 RF switch is responsible for coupling either the Transmitter or the
Receiver subsystem to the probe. This ensures that the sensitive
receiver subsystem is not overloaded with the high powered RF
signal generated by the transmitter system. Also, the receiver is
'blanked' during the transmission and for a short duration
afterward.
 Receiver subsystem: This consists of the components:
Preamplifier, Amplifier, Mixer and the Analog-to-Digital converter
(ADC). The Mixer is used to subtract a reference frequency of
specified phase from the observed signal, resulting a signal of
lower frequency that can be easily digitized.

23.  Field frequency lock
 The field frequency lock consists of a negative
feedback loop that keeps the magnetic field
constant. The superconducting magnets that are
commonly used in high resolution NMR spectrometers
usually have a drift of a few ppb per day (ppb = parts
per billion of the total magnetic field). Many high
resolution multidimensional NMR experiments often
require more than 1 day of measurement. In order to
the ensure that the magnetic field at the sample
stays constant, during this time, an additional small
magnetic field is created by passing current through a
loop of appropriate shape to compensate for the
change in magnetic field due to the main
(superconducting) magnet.

24. • In its first few decades, nuclear magnetic resonance spectrometers used
a technique known as continuous-wave spectroscopy (CW spectroscopy).
This more typically involved using a fixed frequency source and varying
the current (and hence magnetic field) in an electromagnet to observe
the resonant absorption signals. Require only water-cooled
electromagnets instead of the liquid-He-cooled superconducting magnets
found in higher-field FT-NMR spectrometers.
 A cw-NMR spectrometer consists of a control console, magnet, and two
orthogonal coils of wire that serve as antennas for radiofrequency (RF)
radiation. One coil is attached to an RF generator and serves as a
transmitter. The other coil is the RF pick-up coil and is attached to the
detection electronics. Since the two coils are orthogonal, the pick-up coil
cannot directly recieve any radiation from the generator coil. When a
nucleus absorbs RF radiation, it can become reoriented due to its normal
movement in solution and re-emit the RF radiation is a direction that can
be recieved by the pick-up coil. This orthogonal coil arrangement greatly
increases the sensitivity of NMR spectroscopy, similar to optical
fluorescence.
 Spectra are obtained by scanning the magnet and recording the pick-up
coil signal on paper at the control console.

25.  Most applications of NMR involve full NMR spectra, that is, the intensity of the NMR
signal as a function of frequency. Early attempts to acquire the NMR spectrum more
efficiently than simple CW methods involved illuminating the target simultaneously
with more than one frequency. A revolution in NMR occurred when short pulses of
radio-frequency radiation began to be used—centered at the middle of the NMR
spectrum. In simple terms, a short pulse of a given "carrier" frequency "contains" a
range of frequencies centered about the carrier frequency, with the range of
excitation (bandwidth) being inversely proportional to the pulse duration, i.e.
the Fourier transform of a short pulse contains contributions from all the
frequencies in the neighborhood of the principal frequency. X
VVVVVVVVVVVVVVThe restricted range of the NMR frequencies made it relatively
easy to use short (millisecond to microsecond) radio frequency pulses to excite the
entire NMR spectrum.[citation needed]
 Applying such a pulse to a set of nuclear spins simultaneously excites all the single-
quantum NMR transitions. In terms of the net magnetization vector, this corresponds
to tilting the magnetization vector away from its equilibrium position (aligned along
the external magnetic field). The out-of-equilibrium magnetization vector precesses
about the external magnetic field vector at the NMR frequency of the spins. This
oscillating magnetization vector induces a current in a nearby pickup coil, creating
an electrical signal oscillating at the NMR frequency. This signal is known as the free
induction decay (FID), and it contains the vector sum of the NMR responses from all
the excited spins

26. 1:Medicine
 Medical MRI
 Proton NMR and carbon-13 NMR
 Biochemical information can also be obtained
from living tissue (e.g. human brain tumors) with
the technique known as in vivo magnetic
resonance spectroscopy or chemical shift NMR
Microscopy.
 As one of the two major spectroscopic
techniques used in metabolomics, NMR is used to
generate metabolic fingerprints from biological
fluids to obtain information about disease states
or toxic insults.

27. 2:Chemistry
 Structure of compounds: It can be a very selective
technique, distinguishing among many atoms within a
molecule or collection of molecules of the same type but
which differ only in terms of their local chemical
environment.
 Identify known and novel compounds: is usually required
by scientific journals for identity confirmation of
synthesized new compounds.
NMR), since its natural abundance is nearly 100%; isotope
enrichment is required for most other elements.
 Structural dynamics: such as ring-flipping in cyclohexane;
At low enough temperatures, a distinction can be made
between the axial and equatorial hydrogens in
cyclohexane.
 Purity determination (w/w NMR)

28.  Non-destructive testing
 Data acquisition in the petroleum industry
 Quantum computing
 Process control