which is responsible for driving the transitions between the singlet state and central triplet state , as illustrated by |𝑆〉 |𝑇 0 〉 the vector diagram in Figure . Setting we assume that 𝛿𝜔 ≠ 0 the chemical equivalence of the two protons in the complex is broken, giving rise to a non-vanishing difference in their chemical shifts. Alternatively, symmetry breaking can be due to magnetic non-equivalence, i.e., caused by a difference in Jcouplings with other spin-1/2 nuclei present in the complex. In both cases we achieve . The singlet-triplet states are 𝛿𝜔 ≠ 0 introduced in the usual way: