Rotation mutarotation

The optical rotations just cited for each isomer are those measured immediately after each one is dissolved m water On standing the rotation of the solution containing the a isomer decreases from +112 2° to +52 5° the rotation of the solution of the p isomer increases from +18 7° to the same value of +52 5° This phenomenon is called mutarotation What is happening is that each solution initially containing only one anomeric form undergoes equilibration to the same mixture of a and p pyranose forms The open chain form is an intermediate m the process... 

The specific optical rotations of pure a and p o mannopyranose are +29 3° and -17 0° respectively When either form is dissolved in water mutarotation occurs and the observed rotation of the solution changes until a final rotation of +14 2° is observed Assuming that only a and p pyranose forms are present calculate the percent of each isomer at equilibrium... 

A particular carbohydrate can mterconvert between furanose and pyra nose forms and between the a and (3 configuration of each form The change from one form to an equilibrium mixture of all the possible hemi acetals causes a change m optical rotation called mutarotation... 

Mutarotation (Section 25 8) The change in optical rotation that occurs when a single form of a carbohydrate is allowed to equilibrate to a mixture of isomeric hemiacetals... 

Properties. Physical properties of the three crystalline forms of dextrose are Hsted in Table 1. In solution, dextrose exists in both the a- and P-forms. When a-dextrose dissolves in water, its optical rotation, [cc], diminishes gradually as a result of mutarotation until, after a prolonged time, an... 

Both anomers of o-glucopyranose can be crystallized and purified. Pure a-n-glucopyranose has a melting point of 146 °C and a specific rotation, lo-Jn, of +112.2 pure /3-D-glucopyranose has a melting point of 148 to 155 °C and a specific rotation of +18.7. When a sample of either pure anomer is dissolved in water, however, the optical rotation slowly changes and ultimately reaches a constant value of +52.6. That is, the specific rotation of the a-anomer solution decreases from +112.2 to +52.6, and the specific rotation of the /3-anomer solution increases from +18.7 to +52.6. Called mutarotation, this change in optical rotation is due to the slow conversion of the pure anomers into a 37 63 equilibrium mixture. 

Mutarotation (Section 25.5) The change in optical rotation observed when a pure anomer of a sugar is dissolved in water. Mutarotation is caused by the reversible opening and closing of the acetal linkage, which yields an equilibrium mixture of anomcrs. 

Both chondrosamine and D-glucosamine are usually isolated as hydrochlorides but rotational and mutarotational differences between these derivatives are not sufficiently sharp to distinguish between them. The x-ray diffraction pattern is quite distinct for each and the x-ray powder photograph method21 would appear to be the best for identifying small amounts. 

When a sample of pseudo-ir-bromoni trocamphor is dissolved in chloroform a spontaneous change in specific rotation, a, occurs and an equilibrium is established in which the pseudo and normal forms exist. The tabulated data refer to the mutarotation at 14 C (Lowry, J Chem Soc, p 211, 1899). Find the sum of the forward and specific rates, k1+k2. 

D-ribitol (21), and the structure formulated as 2,4-0-benzylidene-D-er-ythrose (22), would be 2,3-O-benzylidene-D-erythrose (23). These reassignments are supported by comparison of the properties of the product described as 22 with data from the literature. Thus, an authentic sample of 22, obtained by a different route (32), had an optical rotation value of — 20 °, which greatly differs from that found for the product formulated (31) as 22 (—65.2° — — 62.6°). The fact that mutarotation is observed, as well as the correspondence with the [a]D value (—62°) for 23, would indicate that the latter is the correct structure for the product described as 22. In any event, hydrolysis of the acetal function of both (22 and 23), leads to D-erythrose. 

The isomerism of a- and jS-glucose is to be attributed to the spatially different arrangement of the H and OH-groups attached to the asymmetric carbon atom 1. This atom is asymmetric in the cyclic lactol formula (Tollens). The mutarotation of the sugars, i.e. the gradual change to the final stationary value of the optical rotation, is to be explained by an equilibrium occurring in solution between the various... 

The acid which was isolated from this salt racemized to zero from an initial activity of [aJc —The occurrence of an opposite direction in the rotation of the free acid as compared with the brucine salt from which-it was isolated is not an uncommon occurrence (51). The brucine salt which was obtained from the filtrate after the insoluble salt was removed gave rise to an inactive acid. This, undoubtedly, was due to mutarotation taking place while the volume of the solution was reduced. 

For a number of optically active ions of the type cis-M(AA)2XY, where M = Co and Cr, there is an initial optical rotation change (mutarotation) that is similar in rate to that of acid hydrolysis, for example,... 

Certain procedures make it possible to obtain the a and 3 anomers of glucose in pure form. A 1-molar solution of a-D-glucose has a rotation value [a]o of +112°, while a corresponding solution of p-D-glucose has a value of +19°. These values change spontaneously, however, and after a certain time reach the same end point of +52°. The reason for this is that, in solution, mutarotation leads to an equilibrium between the a and p forms in which, independently of the starting conditions, 62% of the molecules are present in the P form and 38% in the a form. 

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 ... 

In the case of 3-L-arabinose the strongly positive rotation decreases and the conductivity increment likewise decreases. As A is rather large (for the equilibrium mixture, 119.7), furanoses or hydrates must be taken into account. However, both the constants of the mutarotation and of the change of A correspond very well, namely, k + k = 0.0582,... 

---