Observation of the keto tautomer of d-fructose in D2O using 1H NMR spectroscopy

Abstract

D-Fructose was analysed by NMR spectroscopy and previously unidentified 1H NMR resonances were assigned to the keto and α-pyranose tautomers. The full assignment of shifts for the various fructose tautomers enabled the use of 1H NMR spectroscopy in studies of the mutarotation (5 – 25 °C) and tautomeric composition at equilibrium (5 – 50 °C). The mutarotation of β-pyranose to furanose tautomers in D2O at a concentration of 0.18 M was found to have an activation energy of 62.6 kJ.mol−1. At tautomeric equilibrium (20 °C in D2O) the distribution of the β-pyranose, β-furanose, α-furanose, α-pyranose and the keto tautomers was found to be 68.23%, 22.35%, 6.24%, 2.67% and 0.50%, respectively. This tautomeric composition was not significantly affected by varying concentration between 0.089 and 0.36 M or acidification to pH 3. Upon equilibrating at 6 temperatures between 5 and 50 °C there was a linear relationship between the change in concentration and temperature for all forms.

Analysis of the hydrolysis of inulin using real time 1H NMR spectroscopy

“…42–45 Assignment of the 1 H NMR resonances for inulin in D 2 O has been conducted previously by extensive NMR spectroscopic analyses 43,46 and our own 2D NMR spectroscopic analysis confirmed those assignments. Glucose and fructose 1 H NMR spectroscopic assignments in D 2 O are also available in the literature, 42,47–49 demonstrating that glucose consists of two anomers in solution while fructose equilibrates into at least 5 different tautomers. 50–53 Despite the number of detectable species in solution, sufficiently separated resonances for each species have been identified to make this analysis possible (see supplementary data for tables of 1 H NMR shifts for each carbohydrate discussed).…”

Efficient method of starch functionalization to bis-quaternary structure unit

“…These signals are accounted for proton at secondary alcohol and primary alcohol groups (Fig. 3a) [35]. The complex nature of the spectrum is due to the existence of number of anhydro-glucose units in starch.…”

NMR Spectroscopic Study of Tautomerism in Solution and in the Solid State

“…The equilibria of the tautomeric forms for dissolved fructose (Scheme 5.50) were reinvestigated by 1 H NMR spectroscopy [128]. …”

“…For quantification of the remaining tautomers, protons H-4 [α-pyranose (2.67%), at 3.93-3.97 ppm] and δ ranges [δ(3.88-3.92) -β-pyranose (68.23%), δ(3.54-3.60) -β-furanose (22.35%) and δ(H-5) at 4.06 ppm -α-furanose (6.24%)]were examined[128].…”