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27 Cards in this Set
- Front
- Back
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What is H-1 NMR also known as? |
Proton NMR |
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What are the 4 main features of a proton NMR spectrum? |
The position of the peaks The number of peaks The relative peak area The splitting of each peak |
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Wha does the number of peaks tell us? |
The number of different proton environments |
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What does the relative area under each peak tell us? |
The ratio of hydrogens (relative numbers of protons in each environment. |
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What does the position (chemical shift value) tell us? |
It identifies the type of proton environment present in the molecule |
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What does the splitting pattern tell us and what is the rule? |
The number of non-equivalent proton on the adjacent C atoms to a given proton Splitting pattern= n+1 |
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What type of peak do you get if n=0? |
A singlet peak |
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What type of peak do you get if n=1?
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Doublet |
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What type of peak do you get if n=2?
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Triplet |
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What type of peak do you get if n=3?
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Quartet |
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What type of peak do you get if n=4?
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Multiplet of 5 |
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What information does low resolution H-1 NMR give us? |
The number and type of peaks and the relative area under each peak |
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What is missing from low resolution proton NMR? |
The splitting pattern |
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Which hydrogens can take part in splitting? |
Only those bonded to carbon atoms |
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Why may actual chemical shift values differ from those in the table? |
They may differ depending on their environment |
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How can we manually work out the relative area under each peak (integration trace)? |
Measure the heights as step height is proportional to the are under the peak. Work out the ratio for the heights. Simplify if necessary |
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Which protons should we be wary of in proton NMR? |
-OH or -NH protons |
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Why is this? |
They are exchangeable/labile protons, so they can exchange with the protons in water. |
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What is the chemical shift value for labile protons? |
It can be anywhere, this means it's difficult to identify the bonds |
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What can we use to identify these labile protons? |
We can add D2O (deuterium oxide), which contains a hydrogen isotope called deuterium |
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How does deuterium compare to hydrogen? |
Like hydrogen, it has 1 proton and one electron.However, hydrogen has no neutrons whereas deuterium has 1 |
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Why is D2O used? |
Unlike H-1, H-2 doesn't produce an NMR signal because it has an equal number of neutrons in its nucleus |
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How can we use D2O to identify labile protons? |
We would run proton NMR on the sample and then add a small amount of D2O to another under test. We'd then run a second H-1 NMR on this sample. Any peak due to OH, COOH or NH disappears, so we can identify them by comparing the spectra |
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What must be done to samples before NMR can be performed? |
Samples have to be dissolved in solution, so a solvent is required. |
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Which type of solvents can't be used? |
Organic solvents as the carbon and hydrogen will produce signals that will interfere with the spectrum |
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How do we overcome this? |
We use deuterated solvents e.g. CDCl3 that contain deuterium which doesn't produce a peak on H-1 NMR spectrums |
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What must we do for the carbon spectrum when we use this solvent? |
The carbon peak from the CDCl3 is removed from the spectrum by computer software. |
