![]() The two reagents react with reducing functional groups in unique ways: Benedict’s reagent reacts with aldoses to form a red copper precipitate, while Tollen’s reagent reacts with aldehydes to form a silver, mirrorlike precipitate. Anomers are diastereoisomers of cyclic forms of sugars or similar molecules differing in the configuration at the anomeric carbon (C-1 atom of an aldose or the. carbon atom closest to the ketone functional group. Conversely, non-reducing sugars lack a free anomeric carbon.īenedict’s reagent and Tollen’s reagent are two reagents that are commonly used to detect the presence of reducing sugars. Fructose Fructose is a ketohexose, sugar six members with a ketone group (C. Reducing sugars can be identified through the presence of a free anomeric carbon, meaning it is not in a glycosidic bond and has a free hydroxyl group. Sugars can also be described as being “non-reducing” or “reducing.” A reducing sugar is one that can act as a reducing agent. (The final ratios of each of these forms are usually affected by stereochemistry unique to each molecule.) This tendency to undergo spontaneous cyclization is known as mutarotation. As a result, many sugars can be found in various combinations of D-, L-, and linear forms. ![]() Note that as we convert the structure of the sugar from its two-dimensional to three-dimensional structure, the functional group that is pointing to the right of the Fischer projection will end up pointing downward in the Haworth projection.įor most sugars that are dissolved in a solution, this cyclization occurs spontaneously. A sugar is in its β-anomer form when the anomeric carbon’s substituent is on the same side of the plane as the highest numbered chiral center’s substituent. A sugar is in its α-anomer form when the anomeric carbon’s substituent is on the opposite side of the plane as the highest numbered chiral center’s substituent. Rotate the structure, in order to see the configuration. In a cyclic sugar, the anomeric carbon is the carbon that has two bonds to oxygen.īe aware that a cyclic sugar can exist in two possible anomers: an ⍺-anomer and a β-anomer. The anomeric carbon of fructose is on the left side of the fructose unit rather than the right side. While Fischer projections represent the straight-chain form of carbohydrates, you may also see sugars represented in their cyclic form as Haworth projections. It has not free anomeric carbon atom The anomeric carbons of glucose and galactose are involved in the. If the hydroxyl group of the highest-numbered chiral carbon is on the left, it is in the L-configuration. Sucrose is composed of glucose and fructose. If the hydroxyl group of the highest-numbered chiral carbon is on the right, the sugar is in the D-configuration. For sugars, the absolute configuration is designated using D- and L- nomenclature instead of the R and S system used in organic chemistry.
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