In 2-dimensional or 2D NMR, introducing a second frequency axis enables the identification of coupled spins, yielding connectivity information in a molecule.

First, one of the coupled nuclei is excited during the preparation period.

This is followed by a systematically incremented evolution or wait period, t₁, during which no data is observed.

During the mixing period, a second pulse transfers the magnetization from the excited spins to the coupled nuclei.

Finally, the magnetization of the coupled spins is detected during the acquisition time t₂ for each t₁.

Time domains, t₁ and t₂, are Fourier transformed to yield the frequency domains F1 and F2_, where F1 is usually a chemical shift scale.

Coupling between the same kind of nucleus is studied by homonuclear 2D experiments, whereas heteronuclear 2D experiments investigate the correlation between different nuclei.

2D spectra are generally represented as contour plots where the size of the circles is proportional to the signal intensity.