NMR use in medical science as MRI, Molecular structure determination. Solution structure of proteins and peptides. Magnetic resonance imaging. Identification of protein-protein interaction sites is crucial for understanding the basis of molecular recognition.

1. By -Vivek singh
King George’s Medical University
Lucknow.

2.  Introduction
 Principle and instrumentation
 Resonance( Flipping)
 Population density
 The chemical shift and shielding
 Magnetic anisotropy
 Spin-spin splitting( origin and n+1 rule)
 Application

3.  Nuclei studied by NMR techniques.
 NMR gives information the no. of
magnetically distinct atoms.
 Radiofrequencies have low energy; only
cause nuclear spin[ nmr].

5.  The nucleus has magnetic moment generated
by its charge & spin.
 A hydrogen nuclear may have clockwise
[+1/2] or counterclockwise[-1/2].
 Spin state +1/2 has lower energy and aligned
with magnetic field; -1/2 higher energy
opposite to magnetic field.
 In NMR, entities are nuclear magnetic spins
which populate energy level a/c to quantum
chemical rule.

9.  A slight excess nuclei in lower energy spin state.
 Magnitude of this difference calculated by
BOLTZMANN DISTRIBUTION LAW.
 Saturation achieved if power of RADIOFREQENCY
signal is too high.

10.  Electron surrounds the proton produces
magnetic field which oppose the field
DIAMAGNETIC SHIELDING.
 Standard reference is
TETERAMETHYLSILANE[TMS]-proton are more
shielded than other compounds.
 The CHEMICAL SHIFT is amount by which proton
resonance is shifted from TMS.

11.  Different kinds of protons come at different
chemical shifts.shown below is a chart of
some common kinds of protons that appear
in delta scale.
ppm
TMS
CH3CH3
RONR2
CH3OCH3
RO
HR
R R
HH
RO
Ph CH3
HR
Cl
CH3
Ph
OH
OH
R
NH
R
Upfieldregion
of the spectrum
Downfieldregion
of the spectrum
TMS = Me Si
Me
Me
Me
012345678910
CH3HO
(R)

12.  Area under each peak is proportional to no.
of hydrogens generating that peak.
 Eletronegativity.
 Hybridisation.
 Acidic and exchangeable proton; hydrogen –
bonding.

13.  Downfield= deshielded molecule
 Up field=shielded molecule

14.  Example- benzene;
 It placed in magnetic field, pie electron of
aromatic ring are induced to circulate around
ring.
 Circulation of electron is called ring
current(shielded region).
 Moving electrons generate magnetic field
much like generated in the loop of wire.
 A proton attached to benzene ring is
influenced by three magnetic field(more
deshielded hydrogen).

15.  If a proton has n neighbouring protons that are
equivalent, that proton will split into n+1 lines.
no. of neighbors relative intensities pattern
1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
0
1
2
3
4
5
6
singlet (s)
doublet (d)
triplet (t)
quartet (q)
pentet
sextet
septet
example
H
C C
H
H
C C
H
H
H
C C
H
H
H
H
C CC
H
H
H
H
H
C CC
H
H
HH
H
H
C CC
H
H
H
H
H
H

16.  It arises because hydrogens on adjacent carbon
atoms can SENSE one another.
 n+1 rule-each type of proton senses the no. of
equivalent proton on the carbon atoms next to the
one to which it is bonded and its resonance peak
splits into n+1 components.
C C
HBHA
HA HB
HA is split into tw o lines because
it feels the magnetic field of H B.
HB is split into tw o lines because
it feels the magnetic field of H A.
For this line, H B is lined up
with the magnetic field
(adds to theoverall
magnetic field, so the line
comes at higher frequency)
For this line, H B is lined up
against the magnetic field
(subtracts from the overall
magnetic field, so the line
comes at low er frequency)

17.  When there is more than one proton
splitting a neighbouring proton, we get more
lines. Consider the molecule shown below
where we have 2 protons on one carbon and
one proton on another.
C C
HBHA
HA'
HA + HA' HB
HA and H A' appear at the same
chemical shif t because they are
in identical environments
They are also split into tw o lines
(called a doublet) because they
f eel the magnetic f ield of H B.
HB is split into three lines
because it feels the magnetic
f ield of HA and HA'
Note that the signal produced
by HA + HA' is tw ice the size
of that produced by HB

18.  Molecular structure determination.
 Solution structure of protiens and peptides.
 Magnetic resonance imaging.
 Identification of protien-protien interaction
sites is crucial for understanding the basis of
molecular recognition.