Glucose optical activity

Galactose optically inactive aldaric acid glucose optically active aldaric... 

Both (+) glucose and (+) mannose were oxidized to optically active aldanc acids with nitnc acid... 

Polarimetric determination of the sucrose concentration of a solution is vaUd when sucrose is the only optically active constituent of the sample. In practice, sugar solutions are almost never pure, but contain other optically active substances, most notably the products of sucrose inversion, fmctose and glucose, and sometimes also the microbial polysaccharide dextran, which is dextrorotatory. Corrections can be made for the presence of impurities, such as invert, moisture, and ash. The advantage of polarization is that it is rapid, easy, and very reproducible, having a precision of 0.001°. 

Problem 25.17 I Reduction of D-glucose leads to an optically active alditol (D-glucitol), whereas reduc-I tion of D-galactose leads to an optically inactive alditol. Explain. 

As you can see from their structures, a- and /3-glucose have several chiral carbon atoms. Both isomers are optically active they are not enantiomers (mirror images of one another) because they differ in configuration only at carbon atom 1. As it happens, both a- and /3-glucose rotate the plane of polarized light to the right (clockwise). 

On heating the parent acid of ester VI (from condensation of D-glucose with diethyl 3-oxoglutarate) in aqueous solution,11 following the procedure employed to obtain the corresponding derivative of ethyl acetoacetate XXVI, a sirup results. However, its change in optical activity shows a parallelism with that in analogous cases where crystalline products are isolated, and apparently indicates anhydride formation (see the last line in Table V). 

Tributyl tin radical mediated cyclization of the glucose derived exo-methylene furanose derivatives led to highly functionalized cA-fused bicyclic ethers. The product could subsequently be transformed into optically active tricyclic nucleoside analogue or oxepine derivative (Fig. 51).67... 

Thus, if optically active substance is involved in the reaction, the change in optical rotation can be used directly to follow the progress of reaction. The inversion of sucrose in presence of HC1 giving rise to fructose and glucose can, thus, be monitored polarimetrically. 

We can also nse the term epimer to describe the relationship between isomers, where the difference is in the confignration at jnst one centre (see Section 3.4.4). This is shown for the four epimers of o-(- -)-glucose. An interesting observation with the 16 stereoisomers is that optical activity of a particular isomer does not appear to relate to the confignration at any particnlar chiral centre. 

The dioxirane epoxidation of a prochrral alkene will produce an epoxide with either one new chirality center for terminal alkenes, or two for internal aUcenes. When an optically active dioxirane is nsed as the oxidant, expectedly, prochiral alkenes should be epoxi-dized asymmetrically. This attractive idea for preparative purposes was initially explored by Curci and coworkers in the very beginning of dioxirane chemistry. The optically active chiral ketones 1 and 2 were employed as the dioxirane precursors, but quite disappointing enantioselectivities were obtained. Subsequently, the glucose-derived ketone 3 was used, but unfortunately, this oxidatively labile dioxirane precursor was quickly consumed without any conversion of the aUcene . After a long pause (11 years) of activity in this challenging area, the Curci group reported work on the much more reactive ketone... 

Methacrylic esters of poly hydroxy compounds, like glucose (SO, 51, 136), maltose (136), dextrin (136), starch (136), sorbitol (47, 50, 51) and mannitol (47) derivatives, have also been polymerized however the polymers obtained are mostly insoluble and have not been investigated from the point of view of the relationships between optical activity and structure. 

---