Considered in the laboratory frame, evolution of M B therefore gives rise to two dispersive signals, of opposite phases, at frequencies ω A and ω B (Fig. ). By symmetry, initial B spins exchanging to A during t 1 give rise to identical dispersive signals. In 1D spectra, these signals are not resolved but contribute to the frequency shifts that occur in slow/intermediate exchange, leading to coalescence. However, the dispersive signals can be resolved directly using 2D NMR, as further evolution during t 2 reveals the origin of the signals in t 1 (Fig. ).