Author: Fred J' Grieman

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Magnetic Field Interaction Nuclear Magnetic
Resonance Spectroscopy
Author Fred J. Grieman
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• External Magnetic Field and Spectroscopy (K
  P, 7-12)
• Magnetic dipole created by motion of charge (e.g.
  e- orbital motion, ________)
• External magnetic field ____________
  (Physics of magnetic fields Physics course)
• Orbital Angular Momentum
• A. Splitting of levels due to electric field
  _____________________
• B. Splitting of levels due to magnetic filed
  _____________________
• 1) Magnetic field from small loop of current
  from a large distance
• magnetic dipole. E.g. Atom e- orbit ?
  __________________ (See MS
• 
  
  magnetogyric ratio problems 6
  43-46)
• 2) Interaction with external magnetic field
  Perturbing Hamiltonian
• Hm _______ - ?LBoLz (external field
  along z axis)
• ßB h?L _________________
• Hm?atom -(ßB/h)Bo(z)MLh?atom
• -(ßB)Bo(z)ML?atom

H atom
E
2s,2p
Bo(z)
3
II. ___________________________ Analogous to
orbital ___________________ go 2.0023
(electron g value from relativistic q. m.) In
external magnetic field Em ____________
_______________ Interactions 1) In atom ?LL
?SS ____________________ 2) External field
______________ Spectroscopy of Radical species
III. _________________ (analogous to electron
spin) Spin q. ____ (integer or ½ integer)
mI is z component ______________________
_ e.g., 1H, 13C, 19F - I ½ mI
__________ 2H, 14N - I
1 mI ___________ Em ____________________
gN 1 (must be measured for each nucleus
found in table) ßN me/mNßB ) nuclear
magneton 5.0508 x 10-27 JT-1
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D nucleus I ____
mI _____ mI _____
mI ____ mI ____ mI ____
E
Bo(z)
IV. _______________________________________ Trans
itions between nuclear spin levels Selection
Rules _______________________________ Transition
__________________________ ?o radiofrequency
for typical magnetic fields ?o ? Bo, can vary
either
_________
NMR Spectrometer
Intensity
Fix ?o (400 MHz) and vary Bo Bo for
transition depends on nucleus
_________
RF Generator Detector
____
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Chemistry So far everything derived is for
bare nucleus In molecules, nuclei surrounded
by electrons For diamagnetic molecules, e-s
create magnetic field in opposite direction to
applied external field and proportional to
it ____________________ So magnetic field at
nucleus is ____________________ sj depends
on e- distribution about nucleus j which depends
upon chemical bonding This is the
___________________!!!
mI -1/2 mI 1/2
E
Splitting due to Bj
So transition is now ?o ?Bj
_______________ or Bo(j) _______________
Bo(z)
6
Bo
Bo
Bo
low resolution
CH3OH
Bo
high resolution
Bo
B
Intensity
B(j)
Bo(1-sj)
Bo
Bo
Bo
OH
CH3
Bo(r) Bo(j) Bo(r)
Bo)
d
Bo
7
Bo
Bo
Bo(H)
Bo
Bo(D)
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CH3OH is left as a homework problem Note for
intensities OH mI ?1/2 What about CH3?? 3
equivalent protons, so spins combine
MI SimI(i) of
ways ??? ____
____ ???, ???, ??? ____
____ ???, ???, ??? ____
____ ???
____ ____
CH3OH
____ ____
____ ____ _____ _____
OH
CH3