1. Nuclear Magnetic Resonance (NMR)
Applying Atomic Structure Knowledge to Chemical Analysis

2. 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.

3. 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.

4. # Neutrons AND # Protons are even
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)
EVEN
1, 2, 3, 4, 5, etc.
(integer spin)

5. B 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

6. 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.

7. 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.

8. 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.
H H
H-C - C - OH
CH3 – CH2 – OH 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.

9. Nuclear Magnetic Resonance Spectra: Ethanol
H H
H-C-C-OH
Ethanol: CH3–CH2–OH or
Chemical shift as a ratio to applied magnetic field
This grouping of 3 peaks reflect the 2 hydrogens on the second carbon (methylene hydrogens)
This grouping of 4 peaks reflect the 3 hydrogens on the first carbon (methyl hydrogens) H
- C - H
H-C -
This single peak reflects the hydrogen on the oxygen (hydroxyl hydrogen)
–OH

10. Nuclear Magnetic Resonance Spectra: Ethanol
Chemical shift H
H-C - H
- C -
CH3 – CH2 - OH
Methyl methylene oxygen
Hydrogens hydrogens hydrogen
–OH
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.

11. NMR Applications
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