High field nuclear magnetic resonance spectra of hydroxyl protons of aldoses and ketoses

✍ Scribed by Brigitte Gillet; Daniel Nicole; Jean-Jacques Delpuech; Bernard Gross

• Book ID: 102950884
• Publisher: John Wiley and Sons
• Year: 1981
• Tongue: English
• Weight: 773 KB
• Volume: 17
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1270170108

✦ Synopsis

Abstract

The hydroxyl protons of 23 monosaccharides in their pyranoid from (α or β) are examined by proton NMR at 250 MHz in DMSO‐d~6~ solutions. Intramolecular hydrogen bonding in sugar anions seems to be the major factor in accounting for the lack of parallelism between the pK values and the chemical shifts of the anomeric protons. Another important factor is the possibility of steric hindrance to the solvation of the acidic hydroxyls by the basic DMSO solvent molecules. Equatorial hydroxyls have, as a general rule, lower field chemical shifts (with some exceptions) and larger vicinal HOCH coupling constants, ^3^J, than axial hydroxyls. Moreover, equatorial hydroxyls are sensitive to the equatorial or axial position of their neighbours, in sharp contrast with axial hydroxyls. Long‐range ^4^J couplings are observed whenever a zig‐zag arrangement but a necessary condition is a simultaneous axial position of the OH and CH bonds in the above fragment. In this case, the combined use of vicinal (Karplus‐type equation) and long‐range coupling constants allows the description of the stereochemistry of the OH bond in a semiquantitative fashion.