Glucose specific rotation

Invertase Inverts Sucrose The hydrolysis of sucrose (specific rotation +66.5°) yields an equimolar mixture of D-glucose (specific rotation +52.5°) and D-fructose (specific rotation —92°). (See Problem 4 for details of specific rotation.)... 

D-Glucose can be crystallized in two different forms, a-glucose and p-glucose . The forms have different melting points, and different specific rotations when dissolved in water. These rotations change upon standing to give a solution whose specific rotation is +52.7°. 

The slightly impure product is recrystallized from petroleum ether (b.p. 30-60°) containing 0.5 per cent of anhydrous ether in a continuous extractor, using 100 cc. of solvent per 6-7 g. of compound. One crystallization is generally sufficient to give a pure product. The specific rotation of pure tetiamethyW-glucose prepared by this method is approximately [a] d + 81.3° (Note 4). 

The result, [a] D -f-110° with an error of not more than + 2°, showed that prior to mutarotation the D-glucose was the ordinary a-form of rotation approximately - -109°, now known as a-D-glucopyranose. Sucrose, then, was an a-D-glucoside. Inspection of Fig. 1 also shows that after inversion but before mutarotation the sum of the rotations contributed by the a-D-glucose and the D-fructose remained very close to the specific rotation of 66° possessed by the original sucrose. The relationship ... 

Wohl isolated a hexaacetyl-D-glucose oxime from the mother liquor obtained during the preparation of pentaacetyl-D-glucononitrile. The same acetylated oxime was prepared by Behrend. Wolfrom and Thompson studied it further, and showed conclusively that it possessed a ring structure XI, for it could not be transformed into a nitrile. Because of its low specific rotation, it was assigned to the jS-d series. 

Problem 22.40 Hydrolysis of ( + )-sucrose gives a mixture of d-( + )-glucose ([aji, = 52.7°) and o-(-)-fructose ((ajo = -92.4°) called invert sugar. Calculate the specific rotation of invert sugar. 

One mole of sucrose produces 1 mol each of glucose and fructose, and the specific rotation is one-half the sum of those of the two monosaccharides i.e. 

The term mutarotation means the variation of optical rotation with time, ohserved in a solution of sugar on standing. Let us have a look at this phenomenon in a glucose solution. The pure a anomer of glucose has an m.p. of 146 °C and a specific rotation [a]o +112.2°, and the specific rotation on standing is +52.6°, while pure (3 anomer has an m.p. of 148-155 °C and a specific rotation [a]D + 18.7°, and the specific rotation on standing is + 52.6°. When a sample of either pure anomer is dissolved in water, its optical rotation slowly changes and ultimately reaches a constant value of + 52.6°. Both anomers, in solution, reach an equilibrium with fixed amounts of a (35 per cent), (3 (64 per cent) and open chain ( 1 per cent) forms. 

Sucrose is a disaccharide that is composed of a unit of glucose (acetal form) and a unit of fructose (ketal form) linked through C-1 of glucose and C-2 of fructose, i.e. a 1,2 link. In sucrose, neither glucose nor fructose can exist in open chain form because of the formation of acetal and ketal as shown below. As a result, sucrose is not a reducing sugar, and does now exhibit mutarotation. The specific rotation [a]D of sucrose is +66°. 

Hydrolysis of sucrose yields glucose and fructose with specific rotations [q ]d + 52.5° and —92°, respectively, and makes the resulting mixture laevorotatory (—). This phenomenon of sucrose is called the inversion of sucrose, and the resulting mixture is known as invert sugar, which is the main component of honey, and is sweeter than sucrose itself. 

A freshly prepared solution of a-D-glucose shows a specific rotation of +112°. Over time, the rotation of the solution gradually decreases and reaches an equilibrium value corresponding to [ci ]d5°c = +52.5°. In contrast, a freshly pre-... 

For levulose or fructose, the variations of specific rotation with temperature and concentration are considerable, but the data are somewhat discordant and uncertain, owing to the difficulty of obtaining this sugar pure and crystalline. The value — 930 given in the table, which is in satisfactory agreement with those adopted for glucose and invert sugar, is deduced for about 10% solutions from the formula ... 

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