NMR: Difference between revisions
From Pumping Station One
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= Introductory Theory = | = Introductory Theory = | ||
NMR: | NMR: | ||
Like many types of spectroscopy, NMR ultimately produces a squiggly line on a graph. | Like many types of spectroscopy, NMR ultimately produces a squiggly line on a graph.<br> | ||
* '''Nuclear''' simply means we are concerned with the nucleus of the atoms we are interested in (so the protons and neutrons). With this technique | Breaking down the acronym, we have: | ||
* In essence, any atoms that have an odd number of protons or neutrons (or both) will behave like '''magnets'''. This is due to their '[https://en.wikipedia.org/wiki/Spin_(physics) spin]'. These are commonly referred to as "NMR active" (Common ones being Hydrogen-1 and Carbon-13). | * '''Nuclear''' simply means we are concerned with the nucleus of the atoms we are interested in (so the protons and neutrons). With this technique. In spite of sounding scary, ionizing radiation is not involved in this technique (the actually scary part when you hear the world nuclear). | ||
* In essence, any atoms that have an odd number of protons or neutrons (or both) will behave like '''magnets'''. This is due to their '[https://en.wikipedia.org/wiki/Spin_(physics) spin]'. Only some isotopes of some elements have this property. These are commonly referred to as "NMR active" (Common ones being Hydrogen-1 and Carbon-13). | |||
* By exposing atoms to a magnetic field and RF of a given frequency, we can put them into '''resonance'''. This can be measured, and is the basis for the technique. | * By exposing atoms to a magnetic field and RF of a given frequency, we can put them into '''resonance'''. This can be measured, and is the basis for the technique. | ||
While the nucleus plays a central role in this technique working at all, the configuration of the electrons of an atom in relation to other atoms does play a subtle but very important role in NMR -- [https://www.youtube.com/watch?v=TJhVotrZt9I an atom's configuration of electrons does influence how much an atom is diamagnetically shielded from the effects of RF.]. We use this to our advantage because different electron configurations will resonate at slightly different frequencies. | |||
* Ultimately, you are producing a spectrum | So, in essence, with NMR: | ||
* Ultimately, you are producing a spectrum. | |||
* The height on the Y-Axis predictably represents how much of something there is. | * The height on the Y-Axis predictably represents how much of something there is. | ||
* The X-Axis represents resonance at different frequencies. | * The X-Axis represents resonance at different frequencies. | ||
** If you are performing the typical Hydrogen-1 (Proton NMR) analysis of a sample, | ** If you are performing the typical Hydrogen-1 (Proton NMR) analysis of a sample, the peaks on the X-Axis represents different ways the electrons of a given Hydrogen within a compound are configured. For a simple compound where there is hydrogen in just one configuration (H2O / Water), you'd expect one peak. For Ethanol, CH3-CH2-OH, [https://www.youtube.com/watch?v=CjII0Cg882U we'd expect three peaks]. | ||
One thing to note at this point is that the resonant frequency for a given NMR active nucleus is related to the strength of your NMR's magnetic field. Further, the stronger magnetic field, the greater resolution (sharper peaks) one can achieve. | |||
You will often hear of people referring to the strength of their NMR in terms of MHz (as opposed to the strength of the magnetic field in Tesla). When this is the case, they are typically referring to the frequency of Hydrogen-1 at a given field strength. So, in our case, at 1.4 Tesla, you could say we have a 60MHz NMR. The implication, again, is that it operates at 60MHz when using the Hydrogen-1 probe. The resonant frequency is different if you are analyzing a different nucleus. | |||
== Terminology == | == Terminology == | ||
