Xylose specific rotation

At that time certain 2-desoxyhexoses had been fairly extensively studied, but the only known 2-desoxypentose was 2-desoxy-L-arabinose the specific rotation of which had not been reported. Levene therefore synthesized 2-desoxy-D-xylose and 2-desoxy-L-arabinose. ... 

Specific rotation in aqueous alkali, usually sodium hydroxide. Number-average degree of polymerization (number of xylose residues in the xylan backbone). 0-Acetyl-(4-0-methylglucurono)xylan. In water. 

Specific rotation in aqueous alkali. Crude product, containing 13-14% of xylose residues. 

Fig. 4. Effect of pH on the specific rotations [a] of sugar-molybdate complexes. A L-rhamnose(8), B D-xylose(6), C D-galac-tose(7), D D-glucose(5), E D-arabinose(4) (similar to ref. 16).

The specific rotation of a-xylose is +79° and, after mutarotation, it falls to +19°. Draw the pyranose form that predominates at equilibrium. Similarly, the specific rotation of a-arabinose is +175° and it falls to +104° after mutarotation. Draw the pyranose form that predominates at equilibrium. 

The disaccharide 190a) thus formed reduces Fehling solution it is soluble in water and has a specific rotation in water [a] +94.5°. On hydrolysis with acid it produces one mole of D-glucose and one mole of D-xylose. Oxidation with bromine and subsequent hydrolysis of the oxidation product results in the formation of D-glucose and D-xylonic acid, and shows that the D-xylose constitutes the reducing moiety of the disaccharide. 

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