First-order NMR multiplet

The line pattern obtained when chemically distinguishable spin groups can be treated in the weak-coupling approximation. For an observed spin, each coupled neighbour contributes a frequency displacement of plus or minus half the relevant coupling; coincident lines add intensities.

A first-order pattern combining a doublet splitting with a triplet splitting, commonly from one neighbour and a pair of equivalent neighbours.

Splitting by two distinguishable spin-one-half neighbours with different resolved coupling magnitudes. The four line positions are displaced from the centre by every choice of plus or minus half of each coupling.

Four equally spaced lines can arise from three equivalent neighbours or from coincident couplings to different groups. Combining a doublet with a triplet of the same spacing gives intensities 1:3:3:1; line count alone does not identify a unique topology.