More About Coupling
Earlier we said that protons couple to each other because they feel the magnetic field of the neighboring protons. While this is true, the mechanism by which they feel this field is complicated and is beyond the scope of this class (they don't just feel it through space, it's transmitted through the electrons in the bonds). It turns out that when two protons appear at the same chemical shift, they do not split each other. So, in EtBr, we have a CH3 next to a CH2, and each proton of the CH3 group is only coupled to the protons of the CH2 group, not the other CH3 protons because all the CH3 protons come at the same chemical shift.
