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Nuclear Magnetic Resonance Spectroscopy Workshop
Objectives: By the end of this workshop you will be able to ... describe how n.m.r. spectra are obtained and how they can be used to tell us about the structure of an organic molecule. use low-resolution proton n.m.r. spectra to identify different chemical environments within a molecule (including use of the integration trace and chemical shift values). explain how the fine structure in high-res spectra arises and use it to find the identity of unknown samples (using mass and i.r. spectra as additional evidence where necessary). Throughout this workshop: takes you back to these objectives returns you to the previous page takes you to the next page Home Return Next
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Main Menu Introduction to Nuclear Magnetic Resonance
Interpreting NMR spectra Using spectra to identify molecules Assessment For Learning Task View NMR section in Edexcel A2 Specification Return NMR Chemical Shift data IR data NMR IR Home
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Introduction to Nuclear Magnetic Resonance
What is resonance? A model of magnetic resonance How an NMR spectrometer works Return Magnetic moments! Home Main
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Examples of resonance Return (so what is it?) Home Next
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So what is nuclear magnetic resonance?
Some nuclei can act like little magnets. They will line up with an external field but can be flipped to oppose the field if the correct amount of energy is applied. They will then relax back to their ground state when the energy input ceases. This flipping occurs because atomic nuclei are so small that the alignment is quantised. Return The energy required to resonate the nuclei depends on the element and on the size of the external field, but is usually around 60 – 100 MHz for hydrogen when we carry out NMR. (Radio 1 is 98.8MHz so that would do!) We can investigate what affects this resonant frequency using this equipment ... Home Next
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A model of magnetic resonance
Magnetic stirrer (oscillator) Permanent magnet Compass needle Return Switch on the magnetic stirrer and very slowly increase the frequency of oscillations (i.e. turn its speed up) until you hit the resonant frequency of the compass ... you will see it swing wildly! Home Try achieving the resonance again by fixing the speed (frequency) and moving the permanent magnet closer to increase the field strength. Next
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Investigating magnetic resonance
If you are very careful, you can slowly increase the frequency and get each compass needle to resonate individually. What effect does shielding the compass needle (e.g. with iron) have on the resonance? Return Are the other resonances affected? Home Next
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How an NMR spectrometer works
Return A typical machine for proton NMR will need to operate at 60–100 MHz requiring a field strength of 1.4 – 2.3 Tesla. The high fields at the top end of this range require superconducting magnets which must be cooled by liquid helium. Many modern research NMR machines can run at MHz and there are even 800MHz machines in use with fields of more than 23 Tesla. A 1GHz machine is undergoing tests! Home Next
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NMR spectrometer gallery 1
A 60MHz NMR machine... Return ... and its superconducting 600MHz cousin Home Next
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NMR spectrometer gallery 2
An NMR machine for probing proteins and an 800MHz behemoth! Return Home A medical NMR scanner (MRI machine) Next
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Magnetic moments! 1H Only nuclei with a magnetic moment will be able to undergo nuclear magnetic resonance This means nuclei with an odd number of protons, or an odd number of neutrons ... or both! But what effect does the environment within a molecule have on the resonance? Return Home Menu
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Interpreting Nuclear Magnetic Resonance Spectra
PN1 and PN2 (Low-Resolution) PN2 (Low-Res) and PN3 (High-Res) PN4 PN5 Return PN6 PN7 PN8 PN9 Home NMR Chemical Shift data NMR Main
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Return
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NMR Return Menu
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NMR Return Menu
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NMR Return Menu
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NMR Return Menu
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NMR Return Menu
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NMR Return Menu
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NMR Return Home Main
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Using spectra to identify organic molecules
For each task you will be given the mass, proton nmr and infrared spectrum of an unknown organic molecule. Discuss the data with your partner and attempt to determine the molecule. Be prepared to give evidence for your structure. Help Task 1 Task 2 Task 3 Task 4 Return NMR Chemical Shift data IR data Home NMR IR Main
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Help with tasks The mass spectrum will give you the relative molecular mass. I have marked the parent (molecule) ion on each spectrum with *. You should identify possible fragments (all 1+ ions) for the major peaks. The proton n.m.r. spectrum will indicate the number of different kinds (environments) of hydrogens in your molecule. I have provided the ratio of areas under the peaks and an indication of the splitting pattern in case it is not clearly visible. i.e. 1H 2H etc gives ratio of areas under peaks NMR s = singlet d = doublet t = triplet q = quartet sept = septet m = complex (unresolved) multiplet IR t/d = triplet of doublets etc Main The i.r. spectrum can be used to deduce of confirm the presence of particular bonds (such as carbonyls and hydroxyls) in your molecule. Remember the effect of H-bonding on the infrared spectrum. Return
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Task 1 Help Home NMR Spectrum IR Spectrum Tasks
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Task 1 NMR Help Home Mass Spectrum IR Spectrum Tasks
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Task 1 IR Help Home Mass Spectrum NMR Spectrum Tasks
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Task 2 Help Home NMR Spectrum IR Spectrum Tasks
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Task 2 NMR Help Home Mass Spectrum IR Spectrum Tasks
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Task 2 IR Help Home Mass Spectrum NMR Spectrum Tasks
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Task 3 Help Home NMR Spectrum IR Spectrum Tasks
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Task 3 NMR Help Home Mass Spectrum IR Spectrum Tasks
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Task 3 IR Help Home Mass Spectrum NMR Spectrum Tasks
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Task 4 Help Home NMR Spectrum IR Spectrum Tasks
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Task 4 NMR Help Home Mass Spectrum IR Spectrum Tasks
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Task 4 IR Help Home Mass Spectrum NMR Spectrum Tasks
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Edexcel A2 Specification
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