fares22
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Does the energy required to flip the spin increase as you go down the spectrum, and why is TMS at an energy (ppm) of 0? does this mean that it doesn't require any energy to flip its spin state? Also what determines how far down the spectrum a carbon-13 nucleus is and is it the nuclei as a whole or the seperate nucleons which have the spins and can spin?

Thank you in advance!
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charco
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(Original post by fares22)
Does the energy required to flip the spin increase as you go down the spectrum, and why is TMS at an energy (ppm) of 0? does this mean that it doesn't require any energy to flip its spin state? Also what determines how far down the spectrum a carbon-13 nucleus is and is it the nuclei as a whole or the seperate nucleons which have the spins and can spin?

Thank you in advance!
TMS is set to zero as it is the reference
The whole of the nucleus precesses
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jack_harrison
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(Original post by fares22)
Does the energy required to flip the spin increase as you go down the spectrum, and why is TMS at an energy (ppm) of 0? does this mean that it doesn't require any energy to flip its spin state? Also what determines how far down the spectrum a carbon-13 nucleus is and is it the nuclei as a whole or the seperate nucleons which have the spins and can spin?

Thank you in advance!
As you go further to the left on the spectrum, the required energy to flip the spin state increases, and this is based on the electron density surrounding the nucleus. In simple terms, the electron cloud around a nucleus 'shields' the nucleus from the magnetic field of the spectrometer. So the higher the electron density around the nucleus, the more shielded it is, the less of the magnetic field it 'feels', the lower the energy required to flip the spin state, the smaller the ppm value.

TMS is set to 0ppm by definition as a standard. It has spin states that can be flipped between but all of the ppm values you see are relative to the carbon nucleus in TMS. TMS is only chosen because in most cases, the chemical shift will be higher than that of TMS.

Every nucleon in a nucleus has its own individual spin, the spin of the whole nucleus is simply the sum of all of these spins. The chemical shift is based on the spin states of the entire nucleus.

Hope this helps!
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