ANOMERIC CARBON HOW TO
ANOMERIC CARBON SERIES

ANOMERIC CARBON SERIES

When more than one asymmetrical centre is present in a molecule, as is the case with sugars having four or more carbon atoms, a series of d l pairs exists, and they are functionally, physically, and chemically distinct. In biological systems, only the d or l form may be utilized. Although the initial assignments of configuration for the glyceraldehydes were made on purely arbitrary grounds, studies that were carried out nearly half a century later established them as correct in an absolute spatial sense. It is common, therefore, to designate both, as, for example, d-( l)-fructose or d-( d)-glucose i.e., both have a d-configuration at the centre of asymmetry most remote from the aldehyde end (in glucose) or keto end (in fructose) of the molecule, but fructose is levorotatory and glucose is dextrorotatory-hence the latter has been given the alternative name dextrose. The configurational notation d or l is independent of the sign of the optical rotation of a sugar in solution. **Note that raffinose and stachyose are galactosyl sucroses. *The linkage joins carbon atom 1 (in the β configuration) of one glucose molecule and carbon atom 4 of the second glucose molecule the linkage may also be abbreviated β-1, 4. Representative disaccharides and oligosaccharides All sugars that can be derived from d-glyceraldehyde-i.e., hydroxyl group attached to the asymmetrical carbon atom most remote from the aldehyde or keto end of the molecule projects to the right-are said to be of the d-configuration those sugars derived from l-glyceraldehyde are said to be of the l-configuration. Keto sugars have one less asymmetrical centre for a given number of carbon atoms than do aldehyde sugars.Ī convention of nomenclature, devised in 1906, states that the form of glyceraldehyde whose asymmetrical carbon atom has a hydroxyl group projecting to the right is designated as of the d-configuration that form, whose asymmetrical carbon atom has a hydroxyl group projecting to the left, is designated as l. Similarly, sugars with five carbon atoms have three asymmetrical centres and thus have eight possible isomers (2 3). Sugars containing four carbon atoms have two asymmetrical centres hence, there are four possible isomers (2 2). Since glyceraldehyde has one asymmetrical centre, n is one in the relationship 2 n, and there thus are two possible glyceraldehyde isomers. The position of the hydroxyl group (―OH) attached to the central carbon atom-i.e., whether ―OH projects from the left or the right-determines whether the molecule rotates the plane of polarized light to the left or to the right. In the three-carbon aldose sugar, glyceraldehyde, the asymmetrical centre is located at the central carbon atom. An asymmetrical centre in the case of carbon is defined as a carbon atom to which four different groups are attached. The number of possible structural arrangements for an asymmetrical molecule depends on the number of centres of asymmetry i.e., for n (any given number of) centres of asymmetry, 2 n different isomers of a molecule are possible. Molecules, such as the isomers of glyceraldehyde-the atoms of which can have different structural arrangements-are known as asymmetrical molecules.

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ANOMERIC CARBON HOW TO

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Anomeric carbon