Figure 1.

Schematic illustrating the relation between ${\tilde{\delta }}_H$ and B₀ for a single spin exchanging between two sites with distinct chemical shifts. (a) In the limit $\Delta {\omega }_{\text{X}}\gg k_{\text{ex}}$ the system is in slow exchange and separate peaks are observed at positions that are essentially independent of exchange (${\tilde{\omega }}_{\text{X,G}}$ and ${\tilde{\omega }}_{\text{X,E}}$). (b) In the limit where $\Delta {\omega }_{\mathrm{X}}\ll k_{\text{ex}}$, a single peak is observed at the population weighted average of ${\tilde{\omega }}_{X,E}$ and ${\tilde{\omega }}_{X,G}$. (c,d) As B₀ increases $k_{ex}∕\Delta \omega$ decreases so that the exchanging system moves towards the slow exchange regime and hence ${\tilde{\delta }}_X$ decreases.