Hi everyone. I'm trying to give myself a primer in quantum mechanics/chemistry as I'm doing a literature review on NMR and its applications. I have a few questions. (I'm an electrical engineer, I understand our troubled past, and hopefully our peoples can find a peace) I'm trying to understand chemical shift and just watched the following video on coupling: My first question: Do protons/nuclei transition between spin states? i.e., HA transitions between up an down, thus causing HB to do the same, and that's why there's a doublet? Otherwise if it were stable wouldn't that only result in a singlet? Or is it because different molecules (of which there are millions or billions in a sample) may have on or the other, so it's a net effect? Secondly, the quarks comprising the nucleons contribute little to the actual spin of the nucleus, correct? To my understanding it's primarily a more complicated function of sea quarks as well as electrons? Finally, the MRI world seems to be very different than the NMR spectroscopy world. In MRI they typically talk more of protons, referring to hydrogen nuclei. I understand this is more accurately referring to the hydrogen in water molecules. Given that molecules will orient differently dependent on spin, why do the released energy vectors from nuclei in opposing spins not cancel each other out? I understand that some of these questions may be rudimentary so I apologize in advance. Additionally if responses could be kept fairly plebeian it would be greatly appreciated: while I do have a working knowledge of physics, my quantum physics and mechanics knowledge is amateur at best.