What are the difference between glucose and galactose in H-NMR and C- NMR
Check this out (Bubb, William A., NMR spectroscopy in the study of carbohydrates: Characterizing the structural complexity. Concepts in Magnetic Resonance Part A):
DOI: 10.1002/cmr.a.10080
The difference between Glu and Gal is the configuration at C4. The configuration of Galactose will lead to the neighboring hydrogens to be syn or to have a small dihedral angle and thus result in a smaller H3,H4 and H4, H5 coupling then Glucose where H3,H4 and H4, H5 are anti and will result in a large coupling.
As Clemens Anklin already pointed out, the difference between Glu and Gal is the configuration at C4 and the J-couplings of H4 to H3 and H5 will tell the difference. The challenge is that these couplings are difficult to measure because H3, H4 and H5 heavily overlap and show higher order effects even above 600 MHz also due to the presence of the two anomeric α- and β-forms. The only way to accurately extract these couplings from the 1H-NMR data is a complete computational spectral analysis, which yields the following couplings below. The nice benefit of such an analysis is, that once you know these values, you can easily apply this prior knowledge to subsequent analyses of these compounds at any field.
Please let me know if you have any questions.
- Badges
- Science method