Studies on Ketoses, 1 Distribution of Furanoid and Pyranoid Tautomers of D-Fructose in Water, Dimethyl Sulfoxide, and Pyridinevia1H NMR Intensities of Anomeric Hydroxy Groups in [D6]DMSO
✍ Scribed by Schneider, Bernd ;Lichtenthaler, Frieder W. ;Steinle, Georg ;Schiweck, Hubert
- Publisher
- John Wiley and Sons
- Year
- 1985
- Tongue
- English
- Weight
- 621 KB
- Volume
- 1985
- Category
- Article
- ISSN
- 0947-3440
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✦ Synopsis
In [D,]DMSO the anomeric 2-OH groups of furanoid and pyranoid tautomers O f D-fIUtOSe give distinct. clearly separated singlets, their intensities providing an exact measure of the tautomeric distribution and allowing its determination as a function of temperature and time. Equilibration of tautomers in DMSO being exceedingly slow, this OH-NMR methodology can be applied to detcrmine tautomeric ratios in other solvents, too, by freezing a sample (liquid Nz), dissolution of the resulting ice-matrix in DMSO and rapid recording of the intensities in the low-field OH-region. 'The data obtaincd in this way for aqueous solutions at equilibrium between 0 and 8O'C correlate well with "C NMR-derived values yet are more consistent and considerably more easy to obtain; they cxhibit a clearly linear relationship between equilibrium composition and temperature such that the two fructofuranoses and the a-p-tautomcr increase with temperature on expense of the P-p-form, which at 80°C comprises 550/. at 110°C (i. e. in thc molten state) only 45"h of the tautomers. In pyridinc, the cquilibrium distribution shows a similar linear temperature dependence as does the ratc of equilibration, being nearly nondetectable at 0°C versus essentially instantaneous adaption above 6 0 T , thereby explaining the different outcome of fructose derivatizations in pyridine.
Untersuchungen an
Ketosen, 1. -Verteilung furanoider und pyranoider Tautomerer der D-Fructose in Wasser, Dimethylsulfoxid und Pyridin anhand der 'H-NMR-Intensitaten anomerer Hydroxygruppen in [DJDMSO" In [Do]DMSO ergebcn die anomeren 2-OH-Gruppen der furanoiden und pyranoiden Tautomeren der D-Fructose scharfe, eindeutig getrennte Singuletts, aus deren Intensitat die Tautomerenverteilung in Abhangigkeit von Zeit und Tempcratur genau bestimmt werden kann. Da in DMSO die Equilibrierung auBerst langsam vcrlauft, IZBt sich die OH-NMR-Methodik auf andere Losungsmittel dadurch ubertragen, daD eine Probe cingefrorcn (flussiger N?), die resultiercnde Eismatrix in DMSO-Losung iibergefiihrt und rasch hinsichtlich der OH-Intensitaten vermessen wird. Die so fur waBrige Fructose-1,iisungen zwischcn 0 und.