NMR

definitions etc

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  • Created by: Mia
  • Created on: 20-12-10 14:06

how it occurs

The requirements for NMR Spectroscopy are:

* a strong magnetic field by using an electromagnet

* low-energy radio-frequency radiation

 

Chemical shift: is the scale that compares the frequency of an NMR absorption with the frequency of the reference peak of TMS ag 0ppm

It is measured relative to a reference signal from a standard compound called tetramethylsilane (TMS)

A small amount is added to the spectrometer, it is chemically unreactive and volatile so it can easily be removed from a sample after running NMR.

 

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how it occurs

Deuterium is an isotope of Hydrogen with 1 proton and 1 neutron. It has an even number of nucleons and produces no signal in NMR specta.

CDCL3 is used when running proton and carbon 13 NMR.

so: sample, deuterated solvent (CDCL3) and drop of TMS.

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NMR spectra of OH and NH protons

it can be difficult to identify OH and NH peaks because:

*peaks can appear over a wide range of chemical shift values

*signals are too broad

* no splitting pattern

D20:

*proton spectrum run

* small amount of D20 is added to sample solution and mixture is shaken

* second proton NMR is run and OH or NH peak disappears.

This happens because....

CH3CH2OH + D20 (reverse reaction =..) CH3CH2OD +HOD

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NMR in medicine

NMR used in MRI scans (magnetic resonance imaging)

They are put inside an electromagnet and the protons in their body resonate.

 

Potentially dangerous because the magnetic field is so strong, so people with metal implants can't have this scan.

 

It works because humans have a lot of H+ ions in their body.

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