Homonuclear H Coupling The Simplified Picture

I hope that by now your interest has been piqued. Why do equivalent hydrogens give rise to singlets in some cases and multiplets in others To understand the phenomenon of spin coupling, recall how the magnitude of the effective magnetic field experienced by a nucleus determines its precessional frequency and thereby its chemical shift. If that is not second nature to you by now, perhaps you should review Section 6.1 before proceeding further. 

The number of different spin states (M values) that n equivalent nuclei can adopt is 2nl + 1. Notice that there is only one way to have both up (M = j + j = 1) and one way for both to be down (M- — = but two combinations where one 

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