What does MMR stand for?
Nuclear magnetic
Resonance
How does NMR work?
Molecules in a solution are placed in a strong magnetic field then irradiated with radio frequency . At certain frequencies, the nuclei of some of the atoms in a molecule absorb radio waves
These absorption = resonances used to identify atoms, count them and work out their positions in molecules relative to other atoms their positions in molecules relative to other atoms
What is NMR used for?
used to identify atoms, count them and work out their positions in molecules relative to other atoms their positions in molecules relative to other atoms
what are the 2 main types of NMR
- ¹³C NMR
- ‘H (proton) NMR
How does NMR work (more detail)
• the nucleus of some atoms has nuclear spin (although) many don’t)
• A nucleus with spin generates a small magnetic field
• when a nucleus with spin is placed in a magnetic field, the small magnetic field generated by spin can be aligned with or against the main magnetic field
• there is a difference in energy between the two alignments that corresponds to the energy of radio waves. consequently, if radio waves are passed through the substance, Some frequencies of radio waves will be absorbed to flip the nucleus from one spin to the other .
• this results in a spectrum
Chemical shift
The difference between the absorption in TMS ( a standard) and in the nuclei of a sample compound.
What is TMS
tetramethylsilane
Si(CH³)⁴
Often shown as a peak at 0
It is a comparison tool used to overcome the fact that different spectrometers have different types of magnets and would (otherwise) cause resonance at different frequencies
What are the benefits of using TMS as a standard
- It contains 12 identical protons and gives one strong signal
- It is highly shielded so its peak appears away from the others
- It is non-toxic
- It does not react with the sample
- volatile so easy to remove from the sample
Solvents used in NMR
CDCl3
CCl4
Why is a solvent needed In NMR
NMR analysis is usually carried out in a Solution
Why is CDCl3 a good solvent to be used in H and C NMR Spectroscopy
• It is organic so vdw forces between the molecules and sample
• polar so will dissolve polar samples better than CCl4
•D doesn’t give a peak
Why is CCl4 a good solvent
• Organic molecule
• non-polar
• So vdw forces between the Solvent and sample
What are carbon environments?
Describes the specific chemical surroundings Of a carbon atom within a molecule
Different environments result In different peaks as, due to the different types of atoms bonded to the Carbons, different external magnetic fields are needed to bring them into resonance
What is an integration trace
Line on the NMR spectrum that represents
