Milieu dependence of isomeric composition of D-arabino-hexo-2-ulose in aqueous solution determined by high-resolution NMR spectroscopy.

In this study, high-resolution (1)H NMR spectroscopy (600.03 MHz) and (13)C NMR spectroscopy (150.89 MHz) were used to elucidate the structures of equilibrating d-arabino-hexo-2-ulose (GLUC) (1) isomers in aqueous solution. Four isomers were formed from the investigated ketohexose, and their equilibrium is dependent on the pH value and temperature. Only hydrated GLUC (1) isomers were identified. The (2)C5-β-2,6-pyranoid and the β-2,5-furanoid GLUC (1) isomer were exclusively formed in aqueous solution. Thus, (4)C1-1,5-pyranoid isomers are predominating in the crystalline state. An increase in solution pH or temperature led to a pairwise conversion of configurative information. Thus, changing the measurement conditions permits control over the equilibrium's characteristic. Furthermore, all GLUC (1) isomers showed comparable reaction behavior regarding pH- and temperature-dependent degradation reactions.