NMR

1. A PRESENTATION ON NMR
SPECTROSCOPY
BY KRISHNA TRIPATHI
M.Sc .(PART-1)
ROLL NO.- BT2218

2. ACKNOWLEDGEMENT
I’d want to convey my heartfelt appreciation and gratitude to my professors as well as
my supervisors for providing me with the chance to work on this wonderful project,
which also aided me in conducting extensive study & learning about a bunch of new
topics.
I an quite grateful to them.
Second, I’d want to thank my friends for their assistance in completing this project in
such a short period of time.
It was quiet useful in terms of expanding my knowledge and abilities.
THANK YOU TO EVERYONE WHO HAS HELPED

3. INTRODUCTION:
 Nuclear Magnetic Resonance is a form of absorption spectroscopy.
 It is concern with the absorbtion of radio frequency wave region 4 to 900 Hz by spinning
nuclei in a magnetic field when irradiated by certain energy radiation perpendicular to it.
 Absorption occurs when nuclei undergoes transition from one alignment in the applied field to
the opposite one.
 It thus permits identification configuration in the molecule.

4. CONTENT :
 Introduction
 Spin quantum number
 Principle
 NMR Spectrum
 Instrumentation
 Solvent requirement in NMR
 Relaxation process
 Chemical shift
 Factors influencing chemical shift
 Coupling constant
 Electron nuclear double resonance
 C-13 NMR
 Refrence

5. SPIN QUANTUM NUMBER:
 Spin angular momentum is a spinning charge generates a magnetic field, the resulting spin-
magnet has a magnetic moment (u) proportional to the spin (I).
 According to the quantum theory, a spinning nucleus can only have values for the spin
angular momentum given by the equation.
 Spin angular momentum-[(1+1)]1/2 h/2π
where, I- spin quantum number
h-planks constant
magnetic moment (u) = y X Spin angular momentum
where, y-gyromagnetic ratio.

6.  The gyromagnetic ratio or magnetogyric ratio of a particle or system is the ratio of its
magnetic moment to its angular moment.
 When nuclei place in the magnetic field the energy level become separated corresponding to
m, = -1/2 which is antiparellel to the direction of magnetic fild and the m₂ = +1/2 which is
parallel to the magnetic field for nucleus having spin 1= ½ the energies E, and E2.
E, -½ {yh/ 2π} Ho
E₂ = + ½ {yh/ 2π } Ho
Where
Ho = magnetic field

7.  The frequency at which energy absorbed or emitted is given by the Bohrs relationship.
V= E1-E2/ h
where h-planks constant
 Larmor equation follows that frequency absorb or emitted by a nucleus in moving from one
energy level to another is directly proportional to the applied magnetic field
V=y/2π Ho

8.  Odd mass nuclei with an odd number of nucleons have fractional spins.
 Even mass nuclei with odd numbers of protons and neutrons have integral spins.
 Even mass nuclei composed of even numbers of protons and neutrons have zero spin.( NMR
inactive).

9. PRINCIPLE:
 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 external magnetic field is applied, an energy transfer (AE) 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 gives the NMR spectrum of concerned nucleus.
 The emmited radio frequency is directly proportional to the strength of applied field
v=y/2π Ho
y-gyromagnetic ratio
Ho = magnetic field

10. NMR SPECTRUM:
 NMR spectrum is a plot of intensity of NMR signals VS
magnetic field (frequency) in reference to TMS.

11. INSTRUMENTATION:

12.  Sample holder :- Glass tube with 8.5 cm long to 0.3 cm in diameter.
 Permanent magnet:- It provide homogeneous magnetic field at 60-100 MHz.
 Magnetic coils:- These coils induce magnetic field when current flows through
them.
 Sweep generator :- To produce equal amount of magnetic field pass through the
sample.
 Radio frequency transmitter :- A radio transmitter coil that produces short powerful
pulse of radio waves.
 Radiofrequency receiver :- A radio receiver coils that detect Receiver radio
frequencies emitted as nuclei relax to a lower energy level.
 Readout Device :- A computer that analyses and record the data.

13. SOLVENT REQUIREMENT IN NMR:
 Proton free solvent used which does not show absorbtion of its own in NMR spectrum
 The solvent should be capable of dissolving at least 10% of substance under investigation.
 Characteristic of solvent used
 a-Chemically inert and magnetically isotropic.
 b- It should be devoid of of hydrogen atom.
 c-it should dissolve the sample to a reasonable extent.
 An hydrogen bonding involve electron cloud transfer from hydrogen tom to electronegative
atom (O,N,S.), the hydrogen atom experience deshilding.
 With increase in temperature the extent of hydrogen bonding wan fall result in NMR appear
small & value.

14.  Theire are following solvent was used in NMR spectroscopy...
a-Carbon tetrachloride-(CCL)
b- carbon disulphide - (CS2)
c-Deuterochloroform - CDCI,

15. RELAXATION PROCESS:
 Its the non-radiative transition where the nucleus in the upper transition state returns to the
lower spin state.
 There are three kind of relaxation processes
a- Spin-Spin relaxation - Its due to mutual exchange of spin by two processing nuclei which are
close proximity to each other. It involve transfer of energy from one nucleus to other.
b- Spin- lattice relaxation - It was also known as longitudinal relaxation. It involve the transfer of
the energy from the nucleus in its higher energy state to the molecular lattice. An efficient
relaxation process involves a short time and result in the broadning of absorption peak.
c-Quadrapole relaxation-It is prominent relaxation process for nuclei having I > ½. The nuclei
(such as 14N, 170, 11B etc) due to anisotrophic interaction between non- spherical, electrically
quadrapole nuclei and the electric field gradients at the nucleus caused by electric environments
posses an assymetric positive charge distribution on the nuclei. Hence these nuclei exhibit
electric quadrapole moment and relaxes rapidly. This process known as electric quadrapole
relaxation.

16. RELAXATION PROCESS:
 Its the non-radiative transition where the nucleus in the upper transition state returns to the
lower spin state.
 There are three kind of relaxation processes
a- Spin-Spin relaxation - Its due to mutual exchange of spin by two processing nuclei which are
close proximity to each other. It involve transfer of energy from one nucleus to other.
b- Spin- lattice relaxation - It was also known as longitudinal relaxation. It involve the transfer of
the energy from the nucleus in its higher energy state to the molecular lattice. An efficient
relaxation process involves a short time and result in the broadning of absorption peak.
c-Quadrapole relaxation-It is prominent relaxation process for nuclei having I > ½. The nuclei
(such as 14N, 170, 11B etc) due to anisotrophic interaction between non- spherical, electrically
quadrapole nuclei and the electric field gradients at the nucleus caused by electric environments
posses an assymetric positive charge distribution on the nuclei. Hence these nuclei exhibit
electric quadrapole moment and relaxes rapidly. This process known as electric quadrapole
relaxation.

17. CHEMICAL SHIFT:
 Rotation of electrons about the near by nuclei generates a field that can either oppose or
reinforce the applied field at the proton.
 If the induced field apposes (Diamagnetism) the applied, then the proton is said to be
shielded.
 But if the induced field reinforces applied field (Paramagnetism), the proton feels a higher
field strength and thus, and thus such proton is said to be deshielded.
 Shielding shifts the absorption upfield and deshielding shifts the absorption downfiled to get
an effective field strength neccesary for absorption.
 Tetramethyl silane is taken as standared because of theire less electronegativity.

18.  The difference in the absorption position with respect to TMS signal is
called as chemical shift.
 Delta (5) and tau (1) scale was commonly used for the measurement of
chemical shift. Ŏ express as parts per million and for TMS it taken as 10
and
T=10-δ.
Vsample-Vrefrence operating frequency in megacycles

19. FACTORS INFLUENCING CHEMICAL SHIFT:
 a-Inductive effect - a proton said to be deshielded if it attached with the
 electronegative atom, greater is the deshielding caused to the proton. If deshielding more for
the proton then delta value should be more.
 b- Van der Waal's deshilding - Electron cloud of a bulky group will tend to repel the
 electron cloud surrounding the proton. Thus such a proton deshielded and will resonate at
slightly higher value of delta than expected in the absence of this field.
 Anisotropic effect - The deshielding effect on protons attached to c=c is higher than that can
be accounted for by the inductive effect alone. Aldehyde and aromatic protons are much
more deshielded. Alkyne protons appear at relatively low value of
 d- Hydrogen bonding - If hydrogen atom exhibits the property of hydrogen bonding in a
compound, it will get deshielded due to the strongly electronegative atom attached to it. As
such absorption shif is downfield.
 e- Tempreture and concentration of solution

20.  1H nuclei are shielded by the magnetic field produced by the surrounding
electrons. The higher the electron density around the nucleus, the higher the
magnetic field required to cause resonance.
 Information from 1H-nmr spectra:
1. Number of signals: How many different types of hydrogens in the molecule.
2. Position of signals (chemical shift): What types of hydrogens.
3, Relative areas under signals (integration): How many hydrogens of each type.
4. Splitting pattern: How many neighboring hydrogens

21. COUPLING CONSTANT:
 The distance between the peaks is a given multiple measure of the
magnitude of splitting effect. It is referred to as coupling constant and it is
denoted by symbol J.
 Numerical value of J expressed in Hz or cps.
 Unlike the chemical shifts, the value J was independent of the of the
applied field strength and dependent only upon the molecular structure.

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 NMRspectra. 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 EPR spectrum.

23. ELECTRON SPIN RESONANCE SPECROSCOPY (ESR):
 Provides information about the electronic and molecular structure of paramagnetic
metal centers. Measurement of the spin state, S, the magnitude of hyperfine
interactions with metal and legend nuclei, and the zero-field splitting of half-integer
S> 1/2 electronic states, allows a researcher to identify the paramagnetic center,
and to potentially identify legating atoms.

24. ELECTRON NUCLEAR DOUBLE RESONANCE:
 Electron nuclear double resonance (ENDOR) is a magnetic resonance technique
for elucidating the molecular and electronic structure of paramagnetic species. The
technique was first introduced to resolve interactions in electron paramagnetic
resonance (EPR) spectra.

25. C-13 NMR:
 The 13C nucleus is present in only 1.08% natural abundance. Therefore, acquisition of a spectrum usually
takes much longer than in 'H NMR.
 The magnetogyric ratio of the 13C nucleus is about 1/4 that of the 'H nucleus. Therefore, the resonance
frequency in 13C NMR is much lower than in 'H NMR. 75 MHz for 13C as opposed to 300 MHz for 'H in a
7.04 Tesla field).
 At these lower frequencies, the excess population of nuclei in the lower spin state is reduced which in turn
reduces the sensitivity of NMR detection.
 Unlike 'H NMR, the area of a peak is not proportional to the number of carbons giving rise to the signal.
Therefore, integrations are usually not done.
 Each unique carbon in a molecule gives rise to a 13C NMR signal. Therefore, if there are fewer signals in
the spectrum than carbon atoms in the compound, the molecule must possess symmetry.
 When running a spectrum, the protons are usually decoupled from their respective carbons to give a singlet
for each carbon atom. This is called a proton-decoupled spectrum.

26. REFERENCES:
 Principle of Instrumental Analysis by D.A. Skoog, F. J. Holler and S. R. Crouch
seventh edition Page number 453-493.
 Instrumental method of chemical analysis by G.R.Chatwal and S.K. Anand fifth
edition page number 2.185 to 2.234
 Elementary organic spectroscopy by Y.R. Sharma page number 191 to 250

27. BIBLIOGRAPHY
I Krishna Tripathi of M.Sc 1st year (Biotechnology), have done this project with the
help of my parents, subject teacher & friends.
I used:
1. MS Powerpoint
2. Google Chrome
3. Site: www.sciencedirect.com
For finalizing this project
THANK YOU