Nuclear magnetic resonance spectroscopy:
- It gives you information about the structure using the idea that every atomic nucleus (with an odd number of protons/neutrons) has a
- weak magnetic field due to its nuclear spin, and applying a strong magnetic field will display accordingly.
- Hydrogen is a single proton and so we can use proton NMR to find how many hydrogens there are and how they’re arranged.
Normally protons are spinning randomly, however when you apply a STRONG EXTERNAL MAGNETIC FIELD all the protons line up. Some protons are aligned in the direction of the magnetic field and others are opposing it. Those opposing it are at a higher energy level and can emit a radiowave to move to the lower energy level. Those in the direction of the magnetic field are at a lower energy level and can absorb a radiowave and move to a higher radiowave.
NMR measures the absorption of energy.
Protons in different environments absorb different amounts of energy; due to them being shielded by electrons experiencing the effects of the strong magnetic force instead.
is the difference in absorption of a proton relative to Tetra Methyl Silane (Si(CH3)4).
Where δ = 0 is the value of TMS.
Each peak = one environment. In the graph below, there are two environments (2 peaks)
The less shielded a proton is, the further left the shift will be.
in high res, the peaks of an NMR usually split into smaller peaks, this is because the magnetic field of neighbouring protons interact. The peaks follow an n+1 rule whereby; 2 splits [doublet] = 1 neighbouring proton (or hydrogen)
3 splits [triplet] = 2 neighbouring protons (or hydrogens)
4 splits [quartet] = 3 neighbouring protons (or hydrogens)
- Patient is placed in a very large magnet and irradiated with radio waves
- Hydrogen nuclei in the water in patients body interacts with the radiowaves
- Different frequencies of wave are absorbed by different densities of tissue
- A series of images can be produced by moving the beam to build a 3D image
USES: cancer/bone and joint treatment, brains studies, checking purity in pharmaceutical industry
Pros: non invasive, X-ray would be harmful
1) IR beam goes through sample
2) IR energy is absorbed by the bonds, increasing their energy (vibrational)
3) Different bonds in different environments absorb different wavelengths
4) Any wavelengths that you need to know will be in the data book
in the chemical industry to determine the extent of a reaction by seeing what bonds are present
Drafted by Eunice (Chemistry)