The concept of the presence of a chiral carbon is best described by chirality. What is Chiral Carbon?Ĭhiral carbon atoms are carbon atoms consisting of four single bonds to four different functional groups. That means the hydroxyl group and the exocyclic oxygen atom are on the opposite sides of the molecular projection. The following example shows the alpha anomer of D-glucopyranose.īeta anomer is the configuration of a carbohydrate in which the hydroxyl group is trans to the exocyclic oxygen at the anomeric centre. When we draw a Haworth formula, the hydroxyl group is in the downward direction if it is the alpha anomer. That means the hydroxyl group and the exocyclic oxygen atom are on the same side of the molecular projection. According to the chemical structure of anomeric carbon-containing compounds, there are two types as alpha anomers and beta anomers.Īlpha anomer is the configuration of a carbohydrate in which the hydroxyl group is cis to the exocyclic oxygen at the anomeric centre. Summary – Anomeric Carbon vs Chiral Carbon What is Anomeric Carbon?Īnomeric carbon is the carbon derived from the carbonyl carbon compound of the open-chain form of the carbohydrate molecule. Anomeric Carbon vs Chiral Carbon in Tabular Formĥ. Chiral carbon atoms are carbon atoms consisting of four single bonds to four different functional groups. Acetal derivatives have been prepared by acid-catalyzed reactions with benzaldehyde and acetone.The key difference between anomeric carbon and chiral carbon is that an anomeric carbon atom essentially contains a hydroxyl group that is either cis or trans to the exocyclic oxygen atom, whereas a chiral carbon atom essentially contains four different functional groups attached to it with single covalent bonds.Īnomeric carbon is the carbon originated from the carbonyl carbon compound of the open-chain form of the carbohydrate molecule. A pyranose structure for D-glucose is drawn in the rose-shaded box on the left. The formation of acetal derivatives illustrates how subtle changes may alter this selectivity. Aldolhexoses usually form pyranose rings and their pentose homologs tend to prefer the furanose form, but there are many counter examples. The size of the cyclic hemiacetal ring adopted by a given sugar is not constant, but may vary with substituents and other structural features. Examples of four typical pyranose structures are shown below, both as Haworth projections and as the more representative chair conformers. ![]() We know that these molecules are actually puckered in a fashion we call a chair conformation. These Haworth formulas are convenient for displaying stereochemical relationships, but do not represent the true shape of the molecules. In the D-family, the alpha and beta bonds have the same orientation defined for the furanose ring (beta is up & alpha is down). As with the furanose ring, the anomeric carbon is placed on the right with the ring oxygen to the back of the edgewise view. The cyclic pyranose forms of various monosaccharides are often drawn in a flat projection known as a Haworth formula, after the British chemist, Norman Haworth. ![]() ![]() The upper bond to this carbon is defined as beta, the lower bond then is alpha. The anomeric carbon atom (colored red here) is placed on the right. ![]() By convention for the D-family, the five-membered furanose ring is drawn in an edgewise projection with the ring oxygen positioned away from the viewer. Ribose, an important aldopentose, commonly adopts a furanose structure, as shown in the following illustration. Cyclic structures of this kind are termed furanose (five-membered) or pyranose (six-membered), reflecting the ring size relationship to the common heterocyclic compounds furan and pyran shown on the right. Five and six-membered rings are favored over other ring sizes because of their low angle and eclipsing strain. If necessary, before you attempt to study this section, review the formation of hemiacetals discussed in Section 19.10.Īs noted above, the preferred structural form of many monosaccharides may be that of a cyclic hemiacetal.
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