13C-NMR
In A2/A-Level Chemistry, Carbon-13 has 13 (an odd number!) nucleons, so it produces a signal on an NMR spectrum.
The number of peaks on the spectrum is equal to the number of different carbon environments the molecule contains.
The chemical shift is equal to the type of carbon environment, it can be deduced using a datasheet.
Size of the peak tells us nothing!
1H-NMR
In A2/A-Level Chemistry, the number of peaks on the spectrum is equal to the number of different hydrogen environments the molecule contains.
The chemical shift is equal to the type of hydrogen environment, which can be deduced using a datasheet.
The relative peak area/ integration (ratio/ relative height) is relatively proportional to the number of hydrogens in each environment.
The splitting patter/ multiplet identifies the number of hydrogens on the adjacent carbon – n+1.
(Two NMR spectrum are run one with D2O and one without – the two are compared) When D2O is added we can infer that the peaks that disappear are either –OH or –NH, because the deuterium exchanges with the present hydrogen atom.
Spin-spin coupling
In A2/A-Level Chemistry, Spin-spin coupling (splitting/ producing multiplets) arises from interactions with the spin states of hydrogen atoms on adjacent carbon atoms – this can be used to find the number of hydrogens on the adjacent carbon (structure).
In an external magnetic field each hydrogen atom on the adjacent carbon will either align with or against the external field. If they do align the chemical shift value will increase, if they don’t it will decrease. There are different combinations of up or down spins, if the spin pattern is more probable then the peak will be taller.
NMR in medicine
- NMR can be used to analyse the composition of organic compound during the synthesis of drugs.
- MRI (magnetic (nuclear) resonance imaging) is a technique used to scan a person’s body; it involves resonating the protons in a person’s body by placing them in a large cylindrical electromagnet and exposing them to radio waves. It essentially shows a 3D image of the protons in water or any other hydrogen-containing molecules.
- Areas of the body with the lowest hydrogen atom content, such as bones, show up darker than areas with many hydrogen atoms, such as fatty tissue, which appears brighter.
- In A2/A-Level Chemistry, The brain and spinal cord produce some of the clearest images because they are surrounded by bone tissue. MRI can also show the exact limits of a tumour and whether it has infiltrated surrounding tissue, which helps inform decision for precise surgery, radiotherapy or other treatment. MRI scans can also reveal the extent of sports injuries, such as tears in muscles, tendons and ligament.
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