Why do deshielded protons require more energy in NMR spectroscopy?

[davgonz90]

As you move to the left in the NMR spectrum, the protons become more deshielded. So why is it that they require MORE energy to change their spin? If they don't require more energy, then why is the left side labeled as high frequency? Thanks.

 

[DrDu]

If the protons become deshielded, they see a stronger magnetic field. Hence the energetic difference $\Delta E\sim \mu B$ rises and, by $\Delta E=h\nu$, also frequency.

 

[DrClaude]

The effect of the chemical shielding is to reduce the effective magnetic field at the nucleus. A more deshielded nucleus will have a greater splitting between the different spin orientations, since the splitting is directly proportional to the magnetic field. This leads to a greater transition frequency.

Edit: beaten by DrDu.

 

[davgonz90]

So the frequency refers to amount of energy being absorbed/emitted by the proton? Or the amount of energy in the radiowave being shot at the sample?

 

[DrDu]

It is the amount of energy absorbed by the proton and the energy of the photons of the radiowave.

 

[davgonz90]

Gotcha. You can mark this thread as solved as I understand now. Thanks for your help! :)