Optical rotation of glucose

The distribution between the a and p anomenc forms at equilibrium is readily cal culated from the optical rotations of the pure isomers and the final optical rotation of the solution and is determined to be 36% a to 64% p Independent measurements have established that only the pyranose forms of d glucose are present m significant quanti ties at equilibrium... 

Sucrose, in contrast, is a disaccharide of almost universal appeal and tolerance. Produced by many higher plants and commonly known as table sugar, it is one of the products of photosynthesis and is composed of fructose and glucose. Sucrose has a specific optical rotation, of +66.5°, but an... 

Total hydrolysis of the polymers gave D-glucose only. Water-soluble derivatives (ethyl or carboxymethyl ethers) of the polymers were unaffected by a-amylase, but were partially hydrolyzed by a ceUulase preparation from Acdobader xylinum. The optical rotations of several preparations of this polyglucose and of cellulose (P 1150) in tetraethylammonium hydroxide were all 0°, thereby strongly suggesting that the polyglucoses are /S-D-linked.109... 

Although the crystalline forms of a- and /3-D-glucose are quite stable, in solution each form slowly changes into an equilibrium mixture of both. The process can be observed as a decrease in the optical rotation of the a anomer (+112°) or an increase for the /3 anomer (+18.7°) to the equilibrium value of 52.5°. The phenomenon is known as mutarotation and commonly is observed for reducing sugars. Both acids and bases catalyze mutarotation the mechanism, Equation 20-1, is virtually the same as described for acid- and base-catalyzed hemiacetal and hemiketal equilibria of aldehydes and ketones (see Section 15-4E) ... 

Hemiacetal formation was first observed in optical studies on D-glucose. The optical rotation ([ ) of a freshly dissolved sample of D-glucose changes with time because it possesses two stereoisomeric hemiacetals (anomers) that are interconvertible in solution (fig. 12.5). One of these anomers, a-D-glucose, has [a]D=113 the other, a-L-glucose, has [a]D= 19. The optical rotation of a freshly prepared solution of either of these compounds eventually approaches an intermediate value that depends on the equilibrium between the two anomers. 

An enzyme known as invertase catalyzes the hydrolysis of sucrose to an equimolar mixture of D-glucose and D-fructose. During the hydrolysis, the optical rotation of the solution changes from (+) to (-). What can you conclude from this observation ... 

Specific Rotation Measure the optical rotation of the effluent sample and of the starting Glucose Substrate at 25.0°, and calculate their specific rotations [see Optical (Specific) Rotation, Appendix IIB] by the equation... 

Da Silva et al. " computed the optical rotation of three a and five p conformations of D-glucose in aqueous solution using a TDDFT/GLAO approach with either the aug-cc-pVDZ or 6-31-l-l-G(d,p) basis sets. The a conformations aU have large positive values of [a]o, while the P conformations have values that range from -10° to -1-80°. The Boltzmann-weighted average value is 62.6° or 58.8° with the aug-cc-pVDZ or 6-31-l-l-G(d,p) basis sets, respectively. These values are reasonably close to the experimental value of 52.T For those interested, Mennucci et al. have reviewed the application of computational models of solvent effects on chiroptical properties. 

The optical rotation of a freshly prepared solution of a-D-glucose changes on standing, a phenomenon discovered in 1846 by Dubrun-faut, who stated that if the sugar is dissolved in water at... 

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