spectroscopy 3: magnetic resonance chapter 15. conventional nuclear magnetic resonance energies of...
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Spectroscopy 3:Spectroscopy 3:Magnetic ResonanceMagnetic Resonance
CHAPTER 15CHAPTER 15
Conventional nuclear magnetic resonance Energies of nuclei in magnetic fields
Typical NMR spectrometer
The chemical shift (effect of nearby nuclei)
Fine structure (nuclear spin-spin coupling)
Pulsed techniques in FT-NMR
The 1H-NMR low-resolution spectrum of ethanol
Fig 15.6 The 1H-NMR high-res spectrum of ethanol
Integrated signal
singlet
quartet
triplet
1
3
2
Fine structure
Fine Structure
• Each magnetic nucleus may contribute to the local field ofadjacent nuclei
• ∴ Resonance frequencies are modified
• Strength of interaction given by the coupling constant, J (Hz)
• J is independent of applied mag field, Bo
Margin pg 526 n equivalent nuclei split adjacent spin(s) into n+1 lines with intensity distribution given by Pascal’s triangle:
Fig 15.15 Origin of the 1:2:1 triplet in the proton
resonance of a –CH3 group from coupling with –CH2 protons
e.g., CH3CH2OH
⇇⇉⇆
⇄B0
⇉ ⇇⇆
⇄
Fig 15.16 Origin of the 1:3:3:1 quartet in the proton
resonance of a -CH2 from coupling with -CH3 protons
e.g., CH3CH2OHB0
Spectrum 1 Empiricial formula C4H8O
Spectrum 2 Empiricial formula C4H8O2
Spectrum 3 Contains C, H, O MW = 72