NMR is one of the few techniques that can provide dynamic information at the atomic level. It is able to do this because NMR parameters, like chemical shift, coupling constants and relaxation rates, are influenced by the immediate atomic environment. If the environment changes, then these NMR parameters are likely to change as well. The rate at which the environment changes affects how the NMR parameters appear in a spectrum. If the change is slower than the time taken to record that parameter then it is called "slow exchange", and multiple values of the NMR parameter are recorded. If the change happens faster than the time taken to record it then it is referred to as "fast exchange", and an averaged NMR parameter is detected. As an example, the temperature dependent chemical shifts of the thyroid hormone thyroxine are discussed below.
