1 Nuclear Magnetic Resonance Nuclear Magnetic Resonance (NMR) Applying Atomic Structure Knowledge to...
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Transcript of 1 Nuclear Magnetic Resonance Nuclear Magnetic Resonance (NMR) Applying Atomic Structure Knowledge to...
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Nuclear Magnetic Resonance
Nuclear Magnetic Resonance (NMR)
Applying Atomic Structure Knowledge to Chemical Analysis
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Nuclear Magnetic Resonance
Nuclear Magnetic Resonance Spectroscopy(NMR)
• Spectroscopy is the study of the interaction of electromagnetic radiation with matter.
• Nuclear Magnetic Resonance Spectroscopy uses the NMR phenomena to study the biological, chemical, and physical properties of matter.
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Nuclear Magnetic Resonance
Nuclear Magnetic Resonance Spectroscopy(NMR)
• 1-D NMR is used to determine the structure of simple molecules.
• 2-D NMR is used to determine the structure of more complicated molecules.
• Solid state NMR is used to determine the molecular structure of solids.
• Time domain NMR is used to study molecular dynamics in solutions.
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Nuclear Magnetic Resonance
Nuclear Magnetic Resonance Spectroscopy
• Atoms are put into a static magnetic field and then exposed to a second, oscillating magnetic field.
• Once in these fields, the nuclei of atoms that do have “spin” interact with the oscillating magnetic field (note: not all nuclei have spin though).
• The interaction is detected and recorded.
• Spin in the nucleus can have the following values:
# Neutrons AND # Protons are even
NO SPIN
# Neutrons + # Protons
ODD 1/2, 3/2, 5/2, 7/2, etc.(half integer spin)
# Neutrons + # Protons
EVEN 1, 2, 3, 4, 5, etc. (integer spin)
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Nuclear Magnetic Resonance
Nuclear Magnetic Resonance Spectroscopy
• A spinning nucleus has more energy when its magnetic field opposes the applied magnetic field (B) than when its magnetic field is aligned with the applied field.
• The gap between these 2 energies is a radio frequency.
• This energy can be adsorbed and re-emitted (relaxed).
• The amount of relaxation energy is characteristic of a particular element in a specific chemical environment.
Energy level of a spinning nucleus not in a magnetic field
B (Applied Magnetic Field)
Energy gap
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Nuclear Magnetic Resonance
Nuclear Magnetic Resonance Spectroscopy
• The difference of the energy levels varies depending on the electrical environment of nucleus (i.e. how much the nuclear charge is shielded by surrounding electrons).
• Because the energy gap varies for the same nucleus in different chemical environments, we can use this property for chemical analysis.
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Nuclear Magnetic Resonance
Nuclear Magnetic Resonance Spectroscopy
• This property is called chemical shift. The more electropositive the nucleus is, the bigger the shift.
• A chemical shift is measured in parts per million (ppm) and is the ratio of the shift energy to the energy of the applied magnetic field.
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Nuclear Magnetic Resonance
Nuclear Magnetic Resonance Spectroscopy
For a Hydrogen-NMR (H-NMR), we investigate the hydrogen atoms in a sample. Look at the following sample spectra of ethanol. Ethanol has the formula C2H6O and has the arrangement of atoms shown below.CH3 – CH2 – OH
H HH-C - C - OH H H
or
Three hydrogen atoms are bonded to the first carbon atom.
The second carbon has two hydrogen atoms bonded to it.
The last hydrogen is bonded to the single oxygen atom.
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Nuclear Magnetic Resonance
Chemical shift as a ratio to applied magnetic field
Nuclear Magnetic Resonance Spectra: Ethanol
Ethanol: CH3–CH2–OH H HH-C-C-
OH H H
or
This grouping of 3 peaks reflects the presence of 2 hydrogens on the neighboring carbon
This single peak reflects the hydrogen on the oxygen (hydroxyl hydrogen)
This grouping of 4 peaks reflects the presence of 3 hydrogens on a neighboring carbon
HH-C - H
H- C - H
–OH
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Nuclear Magnetic Resonance
• The hydrogen bonded to the oxygen has the largest chemical shift (~ 5 on the x-axis).
• Oxygen is very electronegative and “hoards” electrons, leaving the hydrogen bonded to it more positive.
• The more exposed the hydrogen nucleus is, the larger the effective positive charge.
• The strongest positive charge interacts the strongest with the applied magnetic field and has the largest chemical shift.
CH3 – CH2 - OHMethyl methylene oxygenHydrogens hydrogens hydrogen
Chemical shift
Nuclear Magnetic Resonance Spectra: Ethanol
HH-C - H
H- C - H
–OH
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Nuclear Magnetic Resonance
• Life Sciences: clinical Magnetic Resonance Imaging (MRI)
• Agriculture and Food Sciences: identifying food additives
• Biotechnology: using NMR probes during formula processing
• Spectroscopy: analysis of unknowns
• Material Science: identify nanotechnology composites of silicon and different polymers
NMR Applications
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Nuclear Magnetic Resonance
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Nuclear Magnetic Resonance