Common chemical shift ranges for nuclei within carbohydrate residues are:
*Typical H NMR chemical shifts of carbohydrate ring protons are 3–6 ppm (4.5–5.5 ppm for anomeric protons).
*Typical C NMR chemical shifts of carbohydrate ring carbons are 60–110 ppm
In the case of simple mono- and oligosaccharide molecules, all proton signals are typically separated from one another (usually at 500 MHz or better NMR instruments) and can be assigned using 1D NMR spectrum only. However, bigger molecules exhibit significant proton signal overlap, especially in the non-anomeric region (3-4 ppm). Carbon-13 NMR overcomes this disadvantage by larger range of chemical shifts and special techniques allowing to block carbon-proton spin coupling, thus making all carbon signals high and narrow singlets distinguishable from each other.
The typical ranges of specific carbohydrate carbon chemical shifts in the unsubstituted monosaccharides are:
*Anomeric carbons: 90-100 ppm
*Sugar ring carbons bearing a hydroxy function: 68-77
*Open-form sugar carbons bearing a hydroxy function: 71-75
*Sugar ring carbons bearing an amino function: 50-56
*Exocyclic hydroxymethyl groups: 60-64
*Exocyclic carboxy groups: 172-176
*Desoxygenated sugar ring carbons: 31-40
*A carbon at pyranose ring closure: 71-73 (α-anomers), 74-76 (β-anomers)
*A carbon at furanose ring closure: 80-83 (α-anomers), 83-86 (β-anomers)