Recall that a proton M coupled to one proton X results in a doublet signal for M. However, NMR-active nuclei can be simultaneously coupled to more than one nonequivalent nucleus. When proton M is coupled to protons X and A, such as in styrene oxide, the signal appears as a doublet of doublets. This complex coupling can be depicted by a splitting diagram. For propyl bromide, where protons M are coupled to three methyl and two methylene protons, the splitting diagram predicts a quartet of triplets with twelve lines. If JAM >> JMX, all twelve peaks would be visible. If JAM ≅ 2 JMX, some peaks overlap, their intensities are added, and nine peaks are seen. When JAM ≅ JMX, as observed in propyl bromide, six peaks are observed. So, the relative magnitudes of the J values can cause deviations from the predicted number of peaks and relative intensities.