NMR-Brief
87
Introduction to NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY Prof. A. Ramachandraiah DEPARTMENT OF CHEMISTRY NATIONAL INSTITUTE OF TECHNOLOGY WARANGAL Warangal, 506004 [email protected] Editor, Vidyarthi Chekumuki JANA VIGNANA VEDIKA [email protected]
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Transcript of NMR-Brief
Introduction to NUCLEAR MAGNETIC RESONANCE
SPECTROSCOPY
Prof. A. Ramachandraiah DEPARTMENT OF CHEMISTRY
NATIONAL INSTITUTE OF TECHNOLOGY WARANGAL Warangal, 506004 [email protected]
Editor, Vidyarthi Chekumuki JANA VIGNANA VEDIKA
Isidor Rabi
1944 Nobel Prize in Physics
E. M. Purcell and Felix Bloch The Nobel Prize in Physics 1952
Kurt Wüthrich Koichi Tanaka John B. Fenn
2002 NOBEL in CHEMISTRY
Sir Peter Mansfield Paul C. Lauterbur
2003 NOBEL in Physiology or Medicine
Magnetic Dipole Moment,
L = I= mr2 v/r = mvr
=iA=
GYROMAGNETIC RATIO
= /L = (qvr/2)/mvr = q/2m
= /L =gq/2m
CLASSICAL ARGUMENTS
Angular Momentum is Continuous
Magnetic Dipole Moment, hence, is also Continuous
QUANTUM MECHANICAL ARGUMENTS
Angular Momentum is DISContinuous
Magnetic Dipole Moment, hence, is also
DISContinuous
If you are not confused by Quantum Science, then, you haven't really understood it.
Niels Bohr
ANGULAR MOMENTUM
PROTONS
(Z)
NEUTRONS
MASS
(A)
e.g QUANTUM (I)
EVEN EVEN EVEN 16O8
0
EVEN ODD ODD 13C6 ½ (2n+1)
n=integer
ODD EVEN ODD 23Na11 ½ (2n+1)
n=integer
ODD ODD EVEN 14N7 n
n=integer
I = ½ I = 1
mz= ½
mz= - ½
mz= +1
mz= 0
mz= - 1
I = 3/2 I = 2
mz= 3/2 mz= +2
mz= 0
mz= - 1
mz= +1
mz= -2 mz= -3/2
mz= +1/2
mz= =-1/2
= g [I(I+1)]1/2
= g [I(I+1)]1/2
z = g mz
z = g mz
z - axis
E= H cos = z H
H
z
H
z
E= H cos = z H
E= H cos = z H = mz gH
For mz = + ½ E1/2 = ½ gH
For mz = - ½ E -1/2 = -½ gH
E -1/2 = ½ gH
E 1/2 = -½ gH
E = gH
In an applied magnetic field the spin states have different energies
and therefore different populations.
E -1/2 = ½ gH
E 1/2 = -½ gH
E = gH = h
Nuclei Unpaired Protons Unpaired Neutrons Net Spin (MHz/T)
1H 1 0 1/2 42.58
2H 1 1 1 6.54
31P 1 0 1/2 17.25
23Na 1 2 3/2 11.27
14N 1 1 1 3.08
13C 0 1 1/2 10.71
19F 1 0 1/2 40.08
Hi = α Ho H = Ho - α Ho = Ho(1 – α)
α Ho
Happ
6
0
0 10)(H
HHs
s
Chemical Shift,
=>
• The area under each peak is proportional to the number of protons.
• Shown by integral trace.
Spin-Spin Splitting
The Origin of 1H NMR—Spin-Spin Splitting
CH3CH2OH
Image:Pacific Northwest National Laboratory 800 MHz NMR Spectrometer.jpg
Hydrogen and Carbon Chemical Shifts
=>
