Direct carbon-proton coupling constants are used to study the anomeric configuration of a sugar.
Vicinal proton-proton coupling constants are used to study stereo orientation of protons relatively to the other protons within a sugar ring, thus identifying a monosaccharide.
Vicinal heteronuclear H-C-O-C coupling constants are used to study torsional angles along glycosidic bond between sugars or along exocyclic fragments, thus revealing a molecular conformation.
Sugar rings are relatively rigid molecular fragments, thus vicinal proton-proton couplings are characteristic:
*Equatorial to axial: 1–4 Hz
*Equatorial to equatorial: 0–2 Hz
*Axial to axial non-anomeric: 9–11 Hz
*Axial to axial anomeric: 7–9 Hz
*Axial to exocyclic hydroxymethyl: 5 Hz, 2 Hz
*Geminal between hydroxymethyl protons: 12 Hz