AB Multiplet

AB quartets are common patterns in molecules containing two isolated protons coupled to each other. A number of protecting groups (Bn, MOM, BOM, PMB, etc) will give AB quartets for CH2O or CH2N groups if they reside in a chiral molecule. AB quartets also show up as subpatterns in ABX, AA'XX' and ABX3 patterns

Four lines are present, with the inner two taller than the outer two. The line intensities are given by:

The coupling constant JAB is calculated as follows:

The chemical shifts of A and B are calculated as follows: