The application of nuclear magnetic resonance to structural studies of carbohydrates in aqueous solution

High‐resolution nuclear magnetic resonance spectroscopy was applied to the study of the structure of carbohydrates in deuterium oxide solution. The structural problems considered were the configuration of anomeric protons, the conformation of pyranoside rings, the preferred ring form, the existence and form of complexes, and the mutarotation of carbohydrates in solution. A modification of the Karplus equation was applied to the calculation of the dihedral angles between the C 1 and C 2 carbon–hydrogen bonds for a number of carbohydrates. A harmonic oscillation of ±15° about the equilibrium dihedral angle was assumed in these calculations. The preferred conformations of several carbohydrates were deduced from the dihedral angles, and an analysis of the diamagnetic susceptibility anisotropy was applied to the predicted conformations in two cases. Observed and calculated shielding differences were determined for each of the ring protons in β‐glucose and β‐mannose. The good agreement obtained from this treatment appears to support the proposed distorted chair and half‐chair conformations for β‐glucose and β‐mannose respectively. Conclusions reached from consideration of NMR spectra were applied to discussions of the stability and structure of several borate complexes and of the preferred ring size of xylose in solution.