Through-bond interaction between nuclear spins that splits NMR resonances. In the weak-coupling limit, equivalent spin- neighbours produce lines with binomial coefficient intensities. Equivalent nuclei do not split each other.
Proton coupling across H-C-C≡C-H can resolve a small four-bond splitting. In a propargyl acetal this connects the acetal methine and terminal alkyne proton.
Through-bond spin coupling involving vinylic nuclei. The geometry of a vicinal pathway across an alkene distinguishes cis and trans coupling.
vicinal coupling between protons on the same side of an alkene. A measured first-order splitting is an approximation if the spin system is appreciably strongly coupled.
vicinal coupling between protons on opposite sides of an alkene. In many ordinary terminal alkenes its magnitude exceeds the corresponding cis coupling.
A set of resonance lines arising from resolved spin coupling. Weak-coupling patterns can be assigned through coupling paths and line intensities; line count alone can be ambiguous.
An approximately six-line scalar-coupling pattern. Similar coupling to five spin-one-half partners can mimic a sextet even when those partners are not all chemically equivalent.
A first-order NMR multiplet produced by coupling to two distinct sets of three equivalent spin-one-half nuclei. Sixteen lines are possible; equal couplings can collapse the pattern to a septet.
A first-order NMR multiplet split into a doublet by one spin-one-half nucleus and into quartets by three equivalent spin-one-half nuclei. Ideally it has eight lines; overlap and second-order behavior can change its appearance.
A first-order NMR multiplet split successively by two distinct spin-one-half couplings and by two equivalent spin-one-half nuclei. Ideally it has twelve resolved lines before coincidences or further unresolved couplings.
A seven-line First-order NMR multiplet. Coupling to six equivalent spin-one-half neighbours gives the intensity ratio .
A four-line first-order pattern, often from three equivalent spin-one-half neighbours, with intensities 1:3:3:1. Equal couplings to different groups can mimic it.
A three-line first-order pattern, often from two equivalent spin-one-half neighbours, with intensities 1:2:1.
A pair of lines with the first-order splitting expected for one spin-one-half neighbour. Additional unresolved or coincident interactions can complicate the pattern.
A resonance with no resolved scalar splitting under the acquisition conditions. This does not prove that every coupling is exactly zero.
Through-bond coupling over a longer path, often four or more bonds. Small resolved allylic couplings can split alkene and oxygen-bound methylene signals and should not be discarded merely because vicinal couplings are larger.
Coupling across an allylic four-bond path, such as between an oxygen-bound CH2 group and terminal vinyl hydrogens in an allyl ester.
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.
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