Nuclear magnetic resonance (NMR) spectroscopy is a technique that exploits the magnetic properties of atomic nuclei to determine the physical and chemical properties of molecules. It is based on the absorption of radiofrequency radiation by atomic nuclei placed in an external magnetic field. NMR provides detailed information about molecular structure by measuring the energies of spin states in atomic nuclei and the spin-spin coupling between them. Modern NMR instruments use Fourier transform techniques to obtain high resolution spectra. Two-dimensional NMR methods such as COSY and NOESY further aid in structural elucidation by correlating nuclei that are coupled or spatially close.

1. NMR SPECTROSCOPY
SUBMITTED BY
SAURABH SHARMA
M.PHARM 1ST SEMESTER
RGPV UNIVERSITY, BHOPAL (M.P.)
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2. Table of contents
• Introduction
• Fundamental principle of NMR
• Instrumentation of NMR
• Interpretation
• Chemical shift
• Number of signals
• Spin-spin coupling: splitting of signals
• Coupling constant
• Integrals
• References
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3. Introduction
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Nuclear Magnetic Resonance (NMR) is a spectroscopy technique which is based on the absorption of
the electromagnetic radiation in the radio frequency region 4 to 900 MHz by nuclei of the atoms.
Nuclear magnetic resonance spectroscopy(NMR) is a powerful analytical technique used to characterize
organic molecules by identifying carbon-hydrogen frameworks within molecules.
It is a research technique that exploits the magnetic properties of certain atomic nuclei.
It determines the physical and chemical properties of atoms or the molecules in which they are
contained.

4. Principle of NMR
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The principle behind NMR is that many nuclei have spin and all nuclei are electrically
charged. If an external magnetic field is applied, an energy transfer is possible
between the base energy to a higher energy level (generally a single energy gap).
The energy transfer takes place at a wavelength that corresponds to radio frequencies
and when the spin returns to its base level, energy is emitted at the same frequency.
The signal that matches this transfer is measured in many ways and processed in order
to yield an NMR spectrum for the nucleus concerned.

5. Energy level diagram
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6. Theory of NMR
The hydrogen nucleus or protons can be regarded as a spinning
positively charged unit and so it will generate a tiny magnetic field
Ho along its spinning axis.
Now if this nucleus is placed in an external magnetic field H0, it will
naturally line up either parallel A or antiparallel B to the direction
of external field. The A will be more stable, being of lower energy.
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7. • The energy difference E between two states will be
absorbed or emitted as the nucleus flips from one
orientation to the other.
Then,
E = hv
where v = a radiation frequency and h = Planck’s
constant
• If correct frequency is applied to the sample
containing hydrogen nuclei and sample is placed in
the external field HQ, then low energy nuclie A will
absorb AE = hv, and flips to B. Thus on flipping back
down, they remit hv as a radiation signal which is
picked up by the instrument.
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8. Effect of magnetic field on atoms
A nucleus is in resonance when it absorbs RF radiation and “spin flips” to a higher energy state.
Thus, two variables characterize NMR: an applied magnetic field B0, the strength of which is measured
in tesla (T), and the frequency n of radiation used for resonance, measured in hertz (Hz), or megahertz
(MHz).
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9. • The frequency needed for resonance and the applied magnetic field strength
are proportionally related:
V α B0
When energy in the form of Radiofrequency is applied and when,
Applied frequency = Processional frequency
• absorption of energy occurs and a NMR signal is recorded .
• The nuclei are said to be in resonance, and the energy they emit when
flipping from the high to the low energy state can be measured.
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10. NMR Instrumentation
Sample holder
Permanent magnet
Magnetic coils
Sweep generator
Radiofrequency transmitter
Radiofrequency receiver
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11. Solvents and reference compounds in NMR
• A substance free from proton should be used as a solvent i.e which does not
give absorption of its own in NMR spectrum. Moreover , the solvent should
be capable of dissolving at least 10% of the substance under investigation.
• Following solvents are commonly used in NMR spectroscopy
1. Carbon tetrachloride (CCl4)
2. Carbon Disulphide (CS4)
3. Deuterochloroform (CDCl3)
4. Hexachloroacetone (CCl3)2CO
• Reference compounds like TMS tetra methyl silane used widely in NMR
spectroscopy.
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12. NMR spectrum
A Spectrum of Absorption of Radiation Vs. Applied
Magnetic Strength is called as NMR Spectrum.
The number of signals shows how many different
kinds of protons are present.
The intensity of the signal shows the number of
protons of each kinds.
The location of the signals shows how shielded or
deshielded the proton is.
Signal splitting shows the number of protons on
adjacent atoms.
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13. Chemical shift
The variations of nuclear magnetic resonance frequencies of the same
kind of nucleus, due to variations in the electron distribution.
CHEMICAL SHIFT=
𝐴𝐵𝑆𝑂𝑅𝑃𝑇𝐼𝑂𝑁 𝐹𝑅𝐸𝑄𝑈𝐸𝑁𝐶𝑌 𝑅𝐸𝐿𝐴𝑇𝐼𝑉𝐸 𝑇𝑂 𝑇𝑀𝑆(𝐻𝑧)
𝑆𝑃𝐸𝐶𝑇𝑅𝑂𝑀𝐸𝑇𝐸𝑅 𝐹𝑅𝐸𝑄𝑈𝐸𝑁𝐶𝑌 (𝑀𝐻𝑧)
𝜔 𝑝𝑝𝑚 =
𝜔 − 𝜔𝑟𝑒𝑓
𝜔𝑟𝑒𝑓
=
𝐻𝑧
𝑀𝐻𝑧
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14. 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.
Chart calibrated versus a reference point, set as 0,
tetramethylsilane [TMS].
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15. 15

16. Shielding
The higher the electron density around the nucleus, the higher the opposing
magnetic field to B0 from the electrons, the greater the shielding.
Because of the proton experiences lower external magnetic field, it needs a
lower frequency to achieve resonance, and therefore, the chemical shift
shifts upfield (lower ppms).
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17. Deshielding
If the electron density around a nucleus decreases, the opposing
magnetic field becomes small and therefore, the nucleus feels
more the external magnetic field B0, and therefore it is said to be
deshielded. Because the proton experiences higher external
magnetic field, it needs a higher frequency to achieve resonance,
and therefore, the chemical shift shifts downfield (higher ppms) .
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18. Factor influencing chemical shift
Both 1H and 13C
Chemical shifts are
related to the
following major
factors:
Depends on
Hydrogen
bonding
Depends on
adjacent
group
Depends on
carbon group
attached
Depends on
hybridization
Depends on
anisotropy
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19. • Molecules having hydrogen bonding have
higher chemical shift and absorb radiation at
low field.
• That is due to the decrease of electronic
density around the nucleus
Hydrogen
Bonding
• For protons on carbon attached to an
electronegative atom or group X( Cl , F ,Br ,I),
the chemical shift increases with the electro
negativity of X. This is due to the inductive
effect on the shielding of the protons and is
apparent in the methyl halides.
Adjacent
Group
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20. Anisotropy
Anisotropy refers to the property of the molecule
where a part of the molecule opposes the applied
field and the other part reinforces the applied field.
Chemical shifts are dependent on the orientation of
neighbouring bonds in particular the π bonds.
Examples of nucleus showing chemical shifts due to π
bonds are aromatics, alkenes and alkynes.
Anisotropic shifts are useful in characterizing the
presence of aromatics or other conjugated structures
in molecules.
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21. Hybridization
In an sp2 C-H bond, the carbon atom has more s character (33% s), which effectively
renders it more electronegative than an sp3 carbon (25% s).
If the sp2 carbon atom holds its electrons more tightly, this results in less shielding for the H
nucleus than in an sp3 bond.
On the basis of hybridization, acetylenic proton to have a chemical shift greater than that of
vinyl proton. But chemical shift of acetylenic proton is less than that of vinyl proton.
Finally sp2 > sp > sp3 .(Order of chemical shift)
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22. Spin- Spin Coupling
Spin-spin coupling is the interaction between
the spin magnetic moments of different electrons and/or
nuclei.
In NMR spectroscopy it gives rise to multiplet patterns, and
cross-peaks in two-dimensional NMR spectra.
Between electron and nuclear spins this is termed the nuclear
hyperfine interaction. Between electron spins it gives rise
to relaxation effects and splitting of the spectrum
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23. FT-NMR
The Fourier Transformation is the basic mathematical calculation necessary to convert
the data in time domain(interferogram) to frequency domain(NMR Spectrum).
Time domain - Intensity v/s Time.
Frequency domain - Intensity v/s Frequency.
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24. Advantages of FT-NMR
Dramatic increase in the sensitivity of NMR measurements.
Has widespread applications esp. for 13C NMR, 31P NMR and 19F NMR giving high signal to noise
ratio facilitating rapid scanning.
Can be obtained with less than 5 mg of the compound.
The signals stand out clearly with almost no electronic background noise.
Used in engineering, industrial quality control and medicine.
MRI is most prominent FT NMR applications.
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25. RELAXATION PROCESS
Relaxation process
involve some non
radiated transition by
which a nucleus in an
upper transition state
return to the lower
spin state. Three kinds
of relaxation process
are:
Spin Spin
relaxation
Spin
lattice
relaxation
Quadra
pole
relaxation
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26. • It is due to the mutual exchange of the spin by two
precessing nuclei which are in close proximity to each other.
It involve the transfer of energy from one nucleus to the
other, there is no net loss of energy.
Spin – Spin
relaxation
• It involve the transfer of energy from the nucleus in its
higher energy state to the molecular lattice. The energy is
transferred to the component of the lattice as the additional
translational, vibrational and rotational energy.
Spin – lattice
relaxation
• It is a prominent relaxation process for nuclei having I > ½.
The nuclei 14N, 17O, 11B etc.
Quadra pole
Relaxation
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27. 2 Dimensional NMR
Two-dimensional nuclear magnetic resonance spectroscopy (2D
NMR) is a set of nuclear magnetic resonance spectroscopy (NMR)
methods which give data plotted in a space defined by two
frequency axes rather than one.
Types of 2D NMR include correlation spectroscopy (COSY), J-
spectroscopy, exchange spectroscopy (EXSY), and nuclear
Overhauser effect spectroscopy (NOESY).
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28. Correlation Spectroscopy (COSY)
It is used to identify spins which are coupled to each other. It
consists of a single RF pulse (p1) followed by the specific
evolution time (t1) followed by a second followed by a
measurement pulse (p2) period (t2).
The two-dimensional spectrum that results from the COSY
experiment shows the frequencies for a single isotope, most
commonly hydrogen (1H) along both axes.
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29. COSY spectra
show two types
of peaks:
A. Diagonal
peaks
B. cross peaks
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30. Nuclear Over- Hauser effect Spectroscopy
(NOESY)
The spectrum obtained is similar to COSY, with diagonal peaks and cross
peaks, however the cross peaks connect resonances from nuclei that are
spatially close rather than those that are through bond coupled to each other.
NOESY spectra also contain extra axial peaks which do not provide extra
information and can be eliminated through a different experiment by
reversing the phase of the first pulse.
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31. Any questions ?
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32. Thank you
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