Spin-spin coupling is the interaction of proton spins through the mediating bonding electrons. The bonding electron pairs its spin with the spin of the nearest proton.

The distance between the peaks in a multiplet is called the coupling constant. The coupling constant is a measure of how strongly a nucleus is affected by the spin states of its neighbor. Its magnetic field is independent of applied field strength.

Structure of trans-1, 3-dichloroprene

1 trans\({{\rm{H}}_{\rm{a}}}\) proton splits the \({{\rm{H}}_{\rm{b}}}\)into \(1 + 1 = 2\)peaks, so it will get a doublet. 2 \({{\rm{H}}_{\rm{c}}}\) protons split \({{\rm{H}}_{\rm{b}}}\)into \(2 + 1 = 3\)peaks, then a doublet of triplets is obtained. Therefore, the splitting diagram for \({{\rm{H}}_{\rm{b}}}\)can be drawn as:

Splitting diagram for \({{\rm{H}}_{\rm{b}}}\)