Nuclear magnetic resonance (NMR) spectroscopy is an analytical technique used to characterize organic molecules by identifying carbon-hydrogen frameworks. It exploits the magnetic properties of certain atomic nuclei when placed in an external magnetic field. 1H NMR is commonly used to determine the type and number of hydrogen atoms in a molecule, while 13C NMR determines the type of carbon atoms. NMR spectra provide information on chemical environments and connectivity between nuclei based on spin-spin coupling patterns. Two-dimensional NMR techniques like HMBC and COSY provide additional structural information through long-range and direct correlations between nuclei.

1. NMR AND ITS KINDS;
HYDROGEN NMR, HMBC, NMR,
H-COSY,NMR

2. INTRODUCTION
• 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.

3. HISTORY
• Nuclear magnetic resonance was first described
by Isidor Rabi in 1938 and in 1944 Rabi was
awarded the Nobel Prize in Physics for this
work.
• In 1946, Felix Bloch and Edward
Mills expanded the technique for use on liquids
and solids, for which they shared the Nobel
Prize in Physics in 1952.

4. NMR INSTRUMENTS
• Sample tube/sample holder
• Permanent magnet
• Magnet coil
• Sweep generator
• Radio frequency transmitter
• Radio frequency reviever.
• Read out system

5. • Sample tube/ sample holder
It should be chemically inert, durable & transparent to NMR
radiation.Generally about 8.5 cm long & approximately 0.3 cm
indiameter isemployed.
•Sample probe
Its the device that hold sample tube in position & is provided
with an air driven turbine for rotating the sample tube almost
100 revolutions per min.

6. •Permanent Magnet
It provide homogenous magnetic field at 60-100MHz.
•Magnetic coil
It induce magnetic field when current flow through them.
Sweep generator To produce equal amount of magnetic field
pass through the sample
•Signal detector & recording system
The electrical signal generated is amplified by means of
amplifier & then recorded.

7. Schematic diagram of NMR

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

9. THEORY OF NMR
• Spin quantum number is related to the atomic and mass number of
the nucleus.
• Elements with odd atomic mass or odd atomic number have the
property of Nuclear Spin.

10. Cont…
• If an external magnetic field is applied the number of possible
orientations can be calculated by:
2I+1 (I= spin quantum number)
Hydrogen has I=1/2 so possible orientations will be two.

11. Principle of NMR
• The theory of NMR comes from
the spin and it generates a
magnetic field.
• Without the application of an
external magnetic field the spin
of elements is random in
direction.
• But when the external magnetic
field is applied nuclei align either
with or against the external
magnet.

13. • 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 and is directly proportional to the strength of the
applied field

14. Chemical Shift
• Is the resonance frequency of a nucleus relative to a standard in a
magnetic field.
• Shielding of protons: High electron density around a nucleus shields
the nucleus from the external magnetic field and the signals are upfield
in the NMR spectrum.
• Deshielding of protons: Lower electron density around a nucleus
deshields the nucleus from the external magnetic field and the signals
are downfield in the NMR spectrum

16. • NMR spectrum is a plot of intensity of NMR signals VS magnetic field
(frequency) in reference to TMS.

17. Acquisition Of Spectra
• The received nuclear magnetic resonance response is very weak in
signal and requires a sensitive radio receiver to pick up.
• Good 1H NMR spectra can be acquired with 16 repeats, which takes
only minutes.
• However, for heavier elements than hydrogen, acquisition of
quantitative heavy-element spectra can be time-consuming, taking
tens of minutes to hours.
• Then a average of all the acquired spectrum will be generated and
displayed through the graph.

18. H NMR
• The most common for of NMR is based on the hydrogen-1 (1H),
nucleus or proton. It can give information about the structure of any
molecule containing hydrogen atoms.
• E.g.,
Ethanol 3 types of CH2,CH3,OH

19. INTERPRETATION OF HNMR
SPECTROMETER
• Number of signals: Indicates how many "different kinds" of protons
are present.
• Position of signals: Indicates something about (chemicalshift)
magnetic (electronic) environment of protons.
• Relative intensity of signals: Proportional to number of protons
present signals.
• Splitting of signals (spin spin coupling): Indicates the number of
nearby nuclei usually protons 13.

20. n+1 rule
• The multiplicity of signal is calculated by using n+1 rule.
• This is one of the rule to predict the splitting of proton signals. This is
considered by the nearby hydrogen nuclei. Therefore, n= Number of
protons in nearby nuclei.
• Zero H atom as neighbour n+1=0+1=1(singlet)
• One H atom as neighbour n+1=1+1 = 2(doublet).
• Two H atom as neighbour n+1=2+1 =3(triplet)

21. Spin-Spin Coupling
• The interaction between the spins of neighbouring nuclei in a
molecule may cause the splitting of NMR spectrum.
• The splitting pattern is related to the number of equivalent H atom at
the nearby nuclei.
• Eg., Ethyl acetate

23. HBMC
• The HMBC (Heteronuclear Multiple Bond Correlation) experiment
gives correlations between carbons and protons that are separated by
two, three and sometimes in conjugated systems, four bonds.
• Direct one-bond correlations are suppressed. This gives connectivity
information much like a proton-proton COSY. The intensity of cross
peaks depends on the coupling constant, which for three-bond
couplings follows the Karplus relationship. For dihedral angles near
90 degrees, the coupling is near zero. Thus, the absence of a cross
peak doesn't confirm that carbon-proton pairs are many bonds apart.

24. • Because of the wide range (0-14 Hz) of possible carbon-proton
couplings, one often does two experiments. One optimized for 5 Hz
couplings and the second optimized for 10 Hz. This gives the optimum
signal-to-noise. Alternatively, a comprise value of 7-8 Hz can be used.
• The spectrum of sucrose at 500 MHz is shown below. The peak
outlined in green shows the two bond correlation between the 2'
carbon and the 1' proton. The peak outlined in red correlates the 6
carbon and 4 proton separated by 3 bonds.

26. H-COSY
• The first and most popular two-dimension NMR experiment is the
“Homonuclear Correlation Spectroscopy (H-COSY)” sequence,
which is used to identify spins which are coupled to each other.
• The two-dimensional spectrum that results from the COSY experiment
shows the frequencies for a single isotope, most commonly hydrogen
(1H) along both axes.

27. • Diagonal peaks correspond to the peaks in a 1D-NMR experiment,
while the cross peaks indicate couplings between pairs of nuclei (much
as multiplet splitting indicates couplings in 1D-NMR).
• COSY spectra show two types of peaks.
• Diagonal peaks have the same frequency coordinate on each axis and
appear along the diagonal of the plot, while
• Cross peaks have different values for each frequency coordinate and
appear off the diagonal.

29. • Different experiments of H-COSY are as follows:
1. COSY-90 is the most common COSY experiment. In COSY-90, the
p1 pulse tilts the nuclear spin by 90°.
2. COSY-45. In COSY-45 a 45° pulse is used instead of a 90° pulse for
the second pulse, p2. The advantage of a COSY-45 is that the
diagonal-peaks are less pronounced, making it simpler to match
cross-peaks near the diagonal in a large molecule.
3. The COSY- 45 is usually the preferred experiment because the
diagonal signals are smaller and less intense allowing correlations
between close resonances to be resolved more easily.

31. THANK YOU