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![]() This flipping of the carbon-13 nucleus from one magnetic alignment to the other by the radio waves is known as the resonance condition. It's possible to detect this interaction between the radio waves of just the right frequency and the carbon-13 nucleus as it flips from one orientation to the other as a peak on a graph. ![]() (BBC Radio 4 is found between 92 - 95 MHz!) If you have also looked at proton-NMR, the frequency is about a quarter of that used to flip a hydrogen nucleus for a given magnetic field strength. The energy needed to make this flip depends on the strength of the external magnetic field used, but is usually in the range of energies found in radio waves - at frequencies of about 25 - 100 MHz. ![]() It is possible to make it flip from the more stable alignment to the less stable one by supplying exactly the right amount of energy. ![]() It is very unstable opposed to the Earth's field, and as soon as you let it go again, it will flip back to its more stable state.īecause a C-13 nucleus behaves like a little magnet, it means that it can also be aligned with an external magnetic field or opposed to it.Īgain, the alignment where it is opposed to the field is less stable (at a higher energy). Provided it isn't sealed in some sort of container, you could twist the needle around with your fingers so that it pointed south - lining it up opposed to the Earth's magnetic field. If you have a compass needle, it normally lines up with the Earth's magnetic field with the north-seeking end pointing north. The effect of this is that a C-13 nucleus can behave as a little magnet. C-13 NMR relies on the magnetic properties of the C-13 nuclei.Ĭarbon-13 nuclei fall into a class known as "spin ½" nuclei for reasons which don't really need to concern us at the introductory level this page is aimed at (UK A level and its equivalents). ![]() On this page we are focussing on the magnetic behaviour of carbon-13 nuclei.Ībout 1% of all carbon atoms are the C-13 isotope the rest (apart from tiny amounts of the radioactive C-14) is C-12. Nuclear magnetic resonance is concerned with the magnetic properties of certain nuclei. This page describes what a C-13 NMR spectrum is and how it tells you useful things about the carbon atoms in organic molecules. ![]()
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