Long-range coupling between protons more than two carbon atoms apart is sometimes observed when ? bonds intervene.

Question:

Long-range coupling between protons more than two carbon atoms apart is sometimes observed when ? bonds intervene. An example is found in 1-methoxy-1-buten-3-yne. Not only does the acetylenic proton, H_a, couple with the vinylic proton H_b, it also couples with the vinylic proton H_C, four carbon atoms away. The data are: Construct tree diagrams that account for the observed splitting patterns of ?H_a? H_b, and H_C