Two-dimensional NMR

Another important development during the 1960s and the 1970s were new magnet designs, based on superconducting materials. They gave higher and more stable magnetic fields leading to spectra with much better sensitivity and resolution. More complex systems could be studied. In order to move to very complicated molecules, however, the next breakthrough was necessary. Inspired by a Belgian scientist Jean Jeener, Ernst and coworkers developed 1975 two-dimensional (2D) FT NMR which introduced many entirely new possibilities.

The diagram illustrates the time course of the one-dimensional (1D) FT NMR method and the 2D FT NMR. In 1D NMR, the nuclear spins are exposed to a pulse, after which a signal is detected in the receiver as a function of time t after the pulse. In 2D NMR, the nuclear spins are subjected to two (or more) pulses, with a time interval t₁. After the second pulse, the signal is acquired in the same way as in 1D NMR, though here we call the time variable t₂. After this, one returns to the beginning of the experiment and repeats it with other values of t₁.

The change of t₁ modfies the signal measured during t₂. This provides a two-dimensional table containing the signal intensity as a function of both t₁ and t₂. After Fourier transformation with respect to both these time variables, one obtains a two-dimensional frequency spectrum in the form of a map showing the dependence of the signal intensity on two frequency variables, denoted F₁ and F₂.