Anomers Monosaccharides that differ

Anomers Monosaccharides that differ in configuration at the hemiacetal OH group (27.6)... 

An extra chiral center is produced at the hemiacetal (or hemiketal) carbon (former carbonyl carbon). The hydroxyl group can be either below (a) or above ( 3) the plane of the ring structure. Monosaccharides that differ only in the configuration of the groups at the hemiacetal (hemiketal) carbon are known as anomers. The hemiacetal (hemiketal) carbon is known as the anomeric carbon (Fig. 122). 

Anomers are stereoisomers of a cyclic monosaccharide that differ in the position of the OH group at the hemiacetal carbon. 

The hemiacetal carbon in a cyclic monosaccharide is the anomeric carbon. Two monosaccharides that differ in configuration only at the anomeric carbon are anomers. 

Compounds that have the same chemical formula but have different structures are called isomers. For example, fructose, glucose, mannose, and galactose are all isomers of each other, having the same chemical formula, C6H1206. If two monosaccharides differ in configuration around only one specific carbon atom (with the exception of the carbonyl carbon, see anomers below), they are defined as epimers of each other. (Of course, they are also isomers ) For example, glucose... 

It is probably no accident that glucose is the most abundant natural monosaccharide because in D-glucose, the larger substituent at each ring carbon is equatorial. The only exception occurs at the anomeric carbon (C-1), where the hydroxyl group maybe axial (in the a anomer) or equatorial (in the /3 anomer). This difference provides one reason why the (3 form is preferred at equilibrium (eq. 16.3). For a ball-and-stick model of /3-D-glucopyranose, see Section 2.9. 

The results established the propensity for stabilizing cooperative structures through multiple hydration and led to a generalization of the mles for conformational selectivity in hydrated monosaccharides [51, 52]. The preference of water molecules for cooperatively bonded conformations of the monosaccharide is such that it can promote conformations which are not favored for the isolated molecule. This is illustrated in the case of the different anomeric forms of Man-O-Ph in Fig. 4b, where the conformations of the isolated and sequentially hydrated monosaccharide, determined from the interpretation of gas-phase IRID spectra, are shown. The a anomer adopts a preferred cG-g+ cooperative conformation. It is unaffected by micro-hydration as water molecules can insert at different sites to increase the cooperative strengthening of the H-bond network. In the p anomer, the equatorial position of 01 turns on the OH2 —> 01 interaction and the preferred... 

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