Nuclear Magnetic Resonance

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Nuclear Magnetic Resonance
Yale Chemistry 800 MHz Supercooled Magnet
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(No Transcript)
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The Precessing Nucleus
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The Precessing Nucleus Again
The Continuous Wave Spectrometer
The Fourier Transform Spectrometer
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Observable Nuclei

• Odd At. Wt. s 1/2
• Nuclei 1H1 13C6 15N7 19F9
  31P15 .
• Abundance () 99.98 1.1 0.385 100
  100

• Odd At. No. s 1
• Nuclei 2H1 14N7

• Unobserved Nuclei
• 12C6 16O8 32S16

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• Thus ?? ?/2?(Bo)

• For a proton,
• if Bo 14,092 gauss (1.41 tesla, 1.41 T),
• ?? 60x106 cycles/sec 60 MHz

• and
• ?EN Nh?? 0.006 cal/mole

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Rf Field vs. Magnetic Field for a Proton
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Rf Field /Magnetic Field for Some Nuclei
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Fortunately, all protons are not created equally!
? (?obs - ?TMS)/?inst(MHz) (240.00 - 0)/60
4.00
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Where Nuclei Resonate at 11.74T
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Chemical Shifts of Protons
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The Effect of Electronegativity on Proton
Chemical Shifts
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Chemical Shifts and Integrals
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Spin-Spin Splitting
anticipated spectrum
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Spin-Spin Splitting
observed spectrum
J is a constant and independent of field
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Spin-Spin Splitting

• 4.4
• J 1.5 Hz

? 6.4 J 1.5 Hz
This spectrum is not recorded at 6 MHz!
??and J are not to scale.
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Multiplicity of Spin-Spin Splitting for s 1/2
multiplicity (m) 2?s 1
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1H NMR of Ethyl Bromide (90 MHz)
CH3CH2Br
for H spins ???????? ????????????????? ???
??????????????? ????????????????????????????
for H spins ????????? ?????????? ??????????????
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1H NMR of Isopropanol (90 MHz)
(CH3)2CHOH
1H septuplet no coupling to OH
(4.25-3.80)x90/6 7.5 Hz
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Proton Exchange of Isopropanol (90 MHz)
(CH3)2CHOH
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Diastereotopic Protons 2-Bromobutane
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Diastereotopic Protons 2-Bromobutane at 90MHz
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1H NMR of Propionaldehyde 300 MHz
No!
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1H NMR of Propionaldehyde 300 MHz
d9.79 (1H, t, J 1.4 Hz)
d1.13 (3H, t, J 7.3 Hz)
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1H NMR of Ethyl Vinyl Ether 300 MHz
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ABX Coupling in Ethyl Vinyl Ether
d3.96 (1H, dd, J 6.9, 1.9 Hz)
d4.17 (1H, dd, J 14.4, 1.9 Hz)
d6.46 (1H, dd, J 14.4, 6.9 Hz)
Another example
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Dependence of J on the Dihedral Angle The
Karplus Equation
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1H NMR (400 MHz) cis-4-t-Butylcyclohexanol
He ?4.03, J(Ha) 3.0 Hz J(He)
2.7 Hz
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1H NMR (400 MHz) trans-4-t-Butylcyclohexanol
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Peak Shape as a Function of ?? vs. J
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Magnetic Anisotropy
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Magnetic Anisotropy
Bo
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13C Nuclear Magnetic Resonance
13C Chemical Shifts
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(No Transcript)
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One carbon in 3 molecules of squalene is 13C
What are the odds that two 13C are bonded to one
another?
10,000 to 1
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13C NMR Spectrum of Ethyl Bromide at 62.8 MHz
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13C NMR Spectrum of Ethyl Bromide at 62.8 MHz
Off resonance decoupling of the 1H region removes
small C-H coupling.
C1
C2
Broadband decoupling removes all C-H coupling.
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0
10
20
ppm (?)
26.6
18.3
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13C Spectrum of Methyl Salicylate (Broadband
Decoupled)
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13C Spectrum of Methyl p-Hydroxybenzoate (Broadban
d Decoupled)
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The 13C Spectrum of Camphor
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The End
F. E. Ziegler, 2004