The Basics of NMR

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The Basics of NMR
- Science Honors Program - Computer Modeling and
Visualization in Chemistry
Eric Knoll
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Nuclear magnetic resonance

• Spectroscopy is the study of the interaction of
  electromagnetic radiation with matter.
• NMR spectroscopy has only been important in
  organic chemistry since the mid-1950s.
• The versatility of NMR makes it pervasive in the
  various fields of science.

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Basis of NMR

• When exposed to a magnetic field, magnetic nuclei
  can receive emit radio waves
• The frequency, ?0 , is proportional to the
  strength, B0 , of the magnetic field
• ?0 2? ?0 ? B0
• ? is the gyro-magnetic ration. It is a
  characteristic constant of the nuclear isotope.

Nuclei Unpaired Protons Unpaired Neutrons Net Spin   (MHz/T)
1H 1 0 1/2 42.58
2H 1 1 1 6.54
31P 0 1 1/2 17.25
23Na 2 1 3/2 11.27
14N 1 1 1 3.08
13C 0 1 1/2 10.71
19F 0 1 1/2 40.08
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Nuclear Spin Classical View
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Macroscopic Magnetization Nuclear Magnetization
in Thermodynamic Equilibrium
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NMR experiment
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Chemical Shift
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Chemical Shift
d (n - nREF) x106 / nREF
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Spin-spin coupling
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Fourier Transform (FT)-I
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Fourier Transform-II
An FT is defined by the integral
                                                 
                                                  
      Think of f(  ) as the overlap of f(t) with
a wave of frequency  .                     
                                                  
     This is easy to picture by looking at the
real part of f(  ) only.                      
                           
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Fourier Transform-III
Consider the function of time, f( t ) cos( 4t )
cos( 9t )
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NMR hardware
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Field strength
Nuclei   (ppm)
A 1.89
B 2.00
C 2.08
Interaction J (Hz)
AB 4
BC 8
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Sample preparation
NMR Lock Solvents NMR Lock Solvents
Acetone CD3COCD3
Chloroform CDCl3
Dichloro Methane CD2Cl2
Methylnitrile CD3CN
Benzene C6D6
Water D2O
Diethylether (DEE) (CD3CD2)2O
Dimethylether (DME) (CD3)2O
N,N-Dimethylformamide (DMF) (CD3)2NCDO
Dimethyl Sulfoxide (DMSO) CD3SOCD3
Ethanol CD3CD2OD
Methanol CD3OD
Tetrehydrofuran (THF) C4D8O
Toluene C6D5CD3
Pyridine C5D5N
Cyclohexane C6H12
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Some examples (1H NMR)
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Integration and of scan
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13C-NMR
Decoupling
Examples
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2-D techniques (COSY)
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Advanced spectroscopic techniques

• Solid-state NMR
• NMR microscopy
• Field-cycling NMR

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The motion involved in NMR spectroscopy is that
of nuclear spin.
  electron   neutron   proton