Magnetic Resonance:

1
Magnetic Resonance Lecture 9 8) High
Resolution NMR of Simple Organic Liquids 8.3
Scalar-Spin-Spin Coupling 8.4 1H NMR
Spectroscopy 8.5 Effect of isotopic
substitution deuteration 8.6 13C
Spectroscopy 8.7 Calculation of NMR spectra from
quantum mechanics and the eigenvalue equation
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Why does the NMR spectrum of ethanol (CH3CH2OH)
have several lines, each resonance line itself
being split?
1H spectra of ethanol (CH3CH2OH)
3

• Chemical shift Chemical environment
• External magnetic field, Bo (Bz k), induces
  movement of electron clouds in molecules,
  inducing a magnetic field opposing Bz k
• Binduced -sBzk
• Effective field experienced by spins
• Beffective (1-s)Bzk
• s is the chemical shift shielding constant
• Zeeman Hamiltonian modified to
• For proton NMR, 1H close to electronegative
  atoms, eg, O or Cl, will be less shielded
  lower value of s, greater Larmor frequency.

4
1H spectra of ethanol (CH3CH2OH)
Intensity of line scales with number of nuclei
v
OH
CH3
CH2

• Scalar Spin-Spin Coupling
• Chemical shift also modified by near-by nuclei,
  causing splitting of resonance lines J-coupling
  or indirect dipolar coupling.