Aldohexoses composition

IV, Composition in Aqueous Solution Aldoses 1. Aldohexoses and Aldopentoses... 

All stereocenters in 1,6-anhydrohexopyranoses are of inverted orientation compared to those in the parent 4Ci(d) or 1C4(l) conformations of the corresponding hexopyranoses for example, see 21, 23, and l,6-anhydro-/J-D-glucopyranose (22). In chemical properties, these compounds resemble to a certain degree the methyl /f-D-hexopyranosides. They are relatively stable in alkaline media, but are readily hydrolyzed by acids. In aqueous acid solution, an equilibrium is established between the 1,6-anhydrohexo-pyranose and the corresponding aldohexose, whose composition correlates with expectations from conformational analysis and calculations from thermodynamic data.121 Extreme values, 0.2 and 86%, are observed respectively with 1,6-anhydro-/f-D-glucopyranose (22) and l,6-anhydro-/f-D-idopyranose (the latter has all hydroxyl groups in equatorial disposition). 

Aldohexoses cyclize in aqueous, mineral acids to give mainly 1,6-anhydrohexopyranoses 1,6-anhydrohexofuranoses are simultaneously formed, but to a far lesser degree (see Sect. IX,1). An equilibrium is established for the 1,6-anhydrohexoses, whose composition can be calculated from thermodynamic data according to Angyal and Dawes99 ... 

Aldopentoses - olive green aldohexoses - blue-grey deoxypentoses - pink to violet deoxyhexoses - yellow to green ketoses - yellow to red for disaccharides colors depend on both composition and linkage... 

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