I have a few questions about NMR.
- Nucleons can spin in an 'up' or 'down' direction and in a nucleus when there is an odd number of nucleons the nucleus then displays an overall spin. Does this overall spin also have a general direction? So, if there was a C-13 isotope, and 6 of its nucleons had an overall 'up' spin and 7 of them had an overall 'down' spin, would the overall spin of the C-13 isotope be 'down'?
- Also would it be correct to say that only nuclei that are aligned with the external magnetic field can resonate by absorbing particular frequencies of radiowaves? ( as those aligned against the external magnetic field are of higher energy and so don't need energy to resonate and become aligned with the external magnetic field?)
- Lastly, if the strength of the external magnetic field is kept constant, are the different chemical environments of the nuclei the only reason that they resonate at different radio wave frequencies to one another?
Any help would really be appreciated, I'm pretty confused about NMR :/
NMR is taught pretty awfully at VCE level tbh.
1. Yes. That's how NMR works; as the overall spin is non-zero, the nucleus as a whole can interact with the external magnetic field. It's a little like asking what's going to happen if you put an electrically neutral object in an electric field. Not much is going to happen there; you'd need some charge somewhere.
2. Yes. The nuclei aligned against and the nuclei aligned with the magnetic field would be in equilibrium (thermodynamically it's actually not stable to have all the nuclei aligned with the magnetic field for reasons I won't go into here; wait until second or third year statistical mechanics for that)
3. Yes. That's the essence of NMR. As different hydrogens (tend to) absorb at different frequencies depending on their chemical environment, NMR allows probing of the number of chemical environments in a molecule, which can be remarkably informing at times.
For instance, if you're given the molecular formula C6H3Cl3 and you're told there's only one H1 NMR peak, that's enough for you to work out a structure already
