NMR - Spectroscopy, Theory & Instrumentation, By Dr. Umesh Kumar Sharma and Shyma . M .S

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NMR -SPECTROSCOPY
Theory , Principle and Instrumentation
By – Dr. UMESH KUMAR SHARMA
& SHYMA M. S.
DEPARTMENT OF PHARMACEUTICS
MAR DIOSCORUS COLLEGE OF PHARMACY,
THIRUVANANTHAPURAM, KERALA, INDIA

2.  Nuclear magnetic resonance (NMR) is a spectroscopic
technique that detects the energy absorbed by changes in the
nuclear spin state.
 NMR spectroscopy is a form of absorption spectrometry.
 Most absorption techniques (e.g.:Ultraviolet-Visible and
Infrared) involve the electrons, in the case of NMR, it is the
nucleus of the atom which determines the response.
 An applied (magnetic) field is necessary for the absorption to
occur.
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3. QUANTUM NUMDERS :
 A number which occurs in the theoretical expression for the
value of some quantized property of a subatomic particle
,atom, or molecule and can only have certain integral or half
integral values.
1. Principal quantum number(n)
2. Angular momentum quantum number(I)
3. Magnetic quantum number(m1)
4. Spin quantum number(s)
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4. PRINCIPAL QUANTUM NUMBER (N) :
 Main energy level occupied by the electrons.
 As n increases, average distance of electron from nucleus
increases.
 Describes the size of the orbital.
 Distance between electron to the nucleus is directly
proportional to the energy of the electron.
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5. ANGULAR MOMENTUM QUANTUM NUMBER(I):
Describes the shape of the orbital.
The three p orbitals are aligned along
perpendicular axes.
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6. MAGNETIC QUANTUM NUMBER (M):
 Describes the orientation around the nucleus or orientation of
orbital.
 For s orbital I=0 and m=0, and if I=1 and m=+1,0,-1 and if I=2
and m=-2,-1,0,+1,+2.
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7. SPIN QUANTUM NUMBER (S) :
 Describes the spin or direction (clockwise or anti clockwise) in
which an electron spin.
 The two possible spin values are +1/2 and -1/2.
Rules of allowed quantum numbers:
 3 quantum number (n, I, m) must be an integer.
 ‘n’ cannot be zero.
 I can be an integer between 0>1>(n-1).
 ‘m’ can be integer between-1>m>+1.
 No two electrons in same atom can have the same four quantum
numbers.
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8. THEORY
 The theory behind NMR comes from the spin of a
nucleus and it generates a magnetic field.
 With out an external applied magnetic field, the nuclear
spin are random in directions.
 But when an an external magnetic field (B0), is present
the nuclei align themselves either with or against the field
of the external magnet.
 When a compound have a proton, proton spin around it’s
own axis & act as a magnet.
 It kept it an external magnetic field it align according to
external magnetic field.
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9. EMR
Beta position
Alpha position
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10. Shielding
Alpha
position
Beta
position
EMR
NN N N N N N N
e-
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11. EMR
De- shielding
Alpha position
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12. PRINCIPLE
• Spinning nucleus
• Effect on external magnetic field
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13. • Precessional motion
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14. • Energy orientation of magnetic dipole
Some of the proton oppose & some align due to the presence of
magnetic field because of different magnetic dipole occurs .The
magnetic dipole represent as (△E)
△E = h
Where:
h = Planck's constant
= frequency of radiation
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15. Precessional frequency α external magnetic field
B0
α
B0
ν
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16. Spin quantum number in NMR
Spin quantum no:= 0 NMR in active
Spin quantum no:= more than 0 NMR active
Atomic
mass
proton neutron Spin
Qu:num:
e.g.
even even even 0 c12
odd odd even ½,2/5, B11
odd even odd ½,2/5 C13
even odd odd 1 N14
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+
up up
dw
Proton
quarts
glucones
Electrical charge in glucones
Up ward = +2e/3
Down ward = -e/3
=+2e/3 +2e/3 –e/3 +
=+1e
p

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Neutron
Up ward = +2e/3
Down ward = -e/3
= +2e/3 –e/3 –e/3
=0

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20. NMR spectrum:
The NMR spectrum is a plot of intensity of NMR signals VS
magnetic field (frequency) in reference to TMS.
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21. INSTRUMENTATION
 Sample holder
 Permanent magnet
 Magnetic coils
 Sweep generator
 Radio frequency transmitter
 Radio frequency receiver
 Read out system
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23. Sample holder:
 Glass tube 8.5 cm long 0.3 cm in diameter.
Permanent magnet:
 It provides homogeneous magnetic field at 60-100 MHZ.
Magnetic coils:
 These coils induce magnetic field when current flows through them.
Sweep generator:
 To produce the equal amount of magnetic field pass through the sample.
Radio frequency transmitter:
 A radio transmitter coil that produces a short powerful pulse of radio waves.
Radio frequency:
 A radio receiver coil that detects receiver radio frequencies emitted as nuclei
relax to a lower energy level.
Readout system:
 A computer that analyses and record the data.

24. SOLVENTS USED IN NMR
The following solvents are normally used in which hydrogen
replaced by deuterium.
 CCI4 - Carbon tetrachloride
 CS2 - Carbon disulfide
 CDCI3 – Deuterio chloroform
 C6D6 – Hexa deuterio benzene
 D2O- Deuterium oxide
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25. NMR RELAXATION
 NMR relaxation is the processes by which an excited magnetic
state returns to its equilibrium distribution.
 NMR relaxation measurement can be used for spectral
assignment and the study of quadrupolar and paramagnetic
interactions, and exchange dynamics.
Types of magnetic relaxation:
Any excited magnetic moment (generally excited by a radio-
frequency pulse) relaxes back to equilibrium on the z-axis. There
are two mechanisms involved:
 spin-lattice
 spin-spin.(Spin-transverse relaxation or T2)
It describes the decay of the excited magnetization perpendicular
to the applied magnetic field (fig.1).
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26. .
Relaxation of magnetization vectors after a 90° pulse.
T1 relaxation along the z-axis in green,
T2 relaxation in the x-y-plane in red
and T1ρ with spin-lock in the x-y-plane in purple.33

27. Ranges of relaxation times:
 Most relaxation times observed in routine NMR are
between 0.1 and 10 seconds.
 Longer relaxation times, tens or hundreds of seconds.
 Shorter relaxation times, milli or microseconds.
Longitudinal or spin-lattice relaxation, T1:
Longitudinal or spin-lattice relaxation (T1) is the mechanism by
which an excited magnetization vector returns to equilibrium
along the axis of the static applied magnetic field
(conventionally shown along the z-axis).
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28. Relaxation via T1 along the magnetic-field (z) axis :
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29. Transverse or spin-spin relaxation, T2:
 Transverse or spin-spin relaxation (T2) is the mechanism by
which the excited magnetization vector (conventionally shown
in the x-y-plane) decays (T2 relaxation mechanism).
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30. REFERENCES
 Instrumental analysis, Skoog, Page.no. 495-509.
 Instrumental method of analysis, Willard Page.no.
422-440.
 Organic spectroscopy, William kemp
 Instrumental methods of chemical analysis,
Chatwal Page.no. 2.190-2.199.
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