Glucopyranose 3 anomer

But there are two chair conformations possible for a D-(+)-glucopyranose anomer 1 and 11 for /3-D-(+)-glucopyranose, for example. 

False Anomers differ in configuration at only the anomeric carbon (Cl). The configurations at the remaining stereocenters (C2 through C5) are the same in a-glucopyranose as they are in /3-glucopyranose. Anomers are therefore diastereomers—not enantiomers—and should not form in equal amounts. Enantiomers differ from each other in configuration at every stereocenter. 

Glucose precipitates from concentrated solutions at room temperature to give crystals that melt at 146°C. Stmctural analysis by X-ray diffraction reveals that these crystals contain only the a-D-(+)-glucopyranose anomer (Figure 24-3). When crystalline a-D-(+)-glucopyranose is dissolved in water and its optical rotation measured immediately, a value = +112... 

Barrows S E, J W Storer, C J Cramer, A D French and D G Truhlar 1998. Factors Controlli Relative Stability of Anomers and Hydroxymethyl Conformers of Glucopyranose. Journal Computational Chemistry 19 1111-1129. 

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. 

Maltose and cellobiose are both reducing sugars because the anomeric carbons on the right-hand glucopyranose units have hemiacetal groups and are in equilibrium with aldehyde forms. For a similar reason, both maltose and cellobiose exhibit mutaiotation of a and /3 anomers of the glucopyranose unit on the right. 

Several 1 -phosphates of deoxyfluoro sugars were prepared, and their acid-catalyzed hydrolysis was studied. 2-Deoxy-2-fluoro- (580), 3-deoxy-3-fluoro- (582), 4-deoxy-4-fluoro- (583), and 6-deoxy-6-fluoro-a-D-gluco-pyranosyl phosphates (584) were prepared by treatment of the corresponding per-( -acetylated )9-D-glucopyranoses with phosphoric acid [the p anomer (581) of 580 was prepared by a different method]. The first and second ionization constants (pA a, and pA a2) of these compounds were determined potentiometrically, as well as by the F-n.m.r. chemical shifts at a series of pH values, and then the rate constants of hydrolysis for neutral (B) and monoanion (C) were decided. The first-order rate-constants (k) for 580-584 and a-D-glucopyranosyl phosphate (in Af HCIO4,25 °) were 0.068, 0.175, 0.480, 0.270, 1.12, and 4.10 (all as x lOVs), respectively. The rate... 

As generally expressed in Section I, derivatives of a-D-glucopyranose are thermodynamically more stable than the /3-d anomers, whereas, for the D-glucofuranoses, the opposite stability of the anomers is observed. This regularity also applies to the respective glycosyl bromides and chlorides. 

The most common activator for the glycosyl sulfoxides is trifluoromethanesulfonic anhydride (triflic anhydride), which, in the absence of nucleophiles, rapidly and cleanly converts most sulfoxides into the corresponding glycosyl triflates in a matter of minutes at —78 °C in dichloromethane solution [86,280,315,316]. In the more extensively studied mannopyranose series, only the a-mannosyl triflate is observed by low-temperature NMR spectroscopy (Scheme 4.35) [280]. In the glucopyranose series, mixtures of a- and (1-triflates are observed, in which the a-anomer nevertheless predominates (Scheme 4.36) [280],... 

Stereospecificity was also encountered in long-range interactions. For 3-deoxy-3-fluoro-D-glucopyranose, the a anomer resonated to... 

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