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24 Cards in this Set
- Front
- Back
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What is NMR?
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An analytical technique for examining molecular structure detail
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What are the requirements for NMR?
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- A strong magnetic field applied using electromagnet
- Low-energy radio-frequency radiation |
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NMR involves the interaction of...
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...materials with the low-energy radiowave region of the electromagnetic spectrum
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What does the number of peaks on a carbon-13 NMR spectrum show?
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The number of carbon environments
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How can you work out the types of carbon environments from a carbon-13 NMR spectrum?
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From the chemical shift
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What does the number of peaks on a proton NMR spectrum tell you?
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The number of proton environments
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What gives the types of proton environment on a proton NMR spectrum?
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The chemical shifts``
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What do the relative peak areas on a proton NMR spectrum show?
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The proportions of protons in each environment
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What gives information about adjacent protons?
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Spin-spin coupling (n+1 rule)
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What is a chemical shift?
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The place in an NMR spectrum at which a nucleus absorbs energy
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What is chemical shift measured relative to?
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A reference signal from a standard compound called TMS
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What is the chemical shift of TMS?
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delta = 0ppm
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What makes TMS easy to remove from a sample after running an NMR spectrum?
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Because TMS is volatile and unreactive
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Why can it be difficult to identify -OH and -NH protons on a NMR spectrum?
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- The peaks can appear of a wide range of different chemical shift values
- The signals are often broad - There's usually no splitting pattern |
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What is deuterium oxide (D2O) this same chemical compound as?
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Water (H2O)
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What is deuterium?
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2D - an isotope of hydrogen
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Why does deuterium not produce an NMR signal?
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It has an even number of nucleons - and odd number is needed for NMR
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How is D2O used in NMR?
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1) A proton NMR spectrum is run
2) A small amount of D2O is added to the sample solution 3) A 2nd proton NMR spectrum is run, and any peak due to -OH or -NH proton will disappear |
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Why do -OH or -NH NMR signals disappear when D2O is added to the sample?
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Because deuterium in D2O exchanges with H present in -OH and -NH; proton exchange
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Why can't an organic solvent be used for NMR spectroscopy?
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Organic solvents contain carbon and hydrogen and these atoms themselves produce a signal
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What kind of solvents are used for NMR spectroscopy?
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Deuterated solvents such as CDCl3 because is produces no signal
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What are the advantages of using MRI compared to X-rays?
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It's harmless and non-invasive because it uses low-energy radio-frequency radiation
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Name some hazards involved when using MRI
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- If a patient has a ferromagnetic metal (Fe, Co, Ni) implant, it can be attracted towards the magnetic in the scanner
- Heart pacemakers are affected by the magnetic field - Anything ferromagnetic, e.g. pens, knives, can fly across the room |
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What image is produce using an MRI? And why is this useful in medicine?
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A 3D NMR Spectrum of protons in water and other hydrogen-containing molecules. Many diseases change the water content within tissues and organs, the scanner can detect these differences.
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