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Seliwanoff’s test is a chemical test which distinguishes between aldose and ketose sugars. If the sugar contains a ketone group, it is a ketose. If a sugar contains an aldehyde group, it is an aldose. This test relies on the principle that, when heated, ketoses are more rapidly dehydrated than aldoses.
However, aldoses are not locked into any one conformation: they can and do fluctuate between different forms. Aldoses can tautomerize to ketoses in a dynamic process with an enol intermediate (more specifically, an enediol). [1] This process is reversible, so aldoses and ketoses can be thought of as being in equilibrium with each other.
Reducing form of glucose (the aldehyde group is on the far right). A reducing sugar is any sugar that is capable of acting as a reducing agent. [1] In an alkaline solution, a reducing sugar forms some aldehyde or ketone, which allows it to act as a reducing agent, for example in Benedict's reagent.
Ketoses and aldoses can be chemically differentiated through Seliwanoff's test, where the sample is heated with acid and resorcinol. [4] The test relies on the dehydration reaction which occurs more quickly in ketoses, so that while aldoses react slowly, producing a light pink color, ketoses react more quickly and strongly to produce a dark red color.
Aldonic acids are the products of the oxidation of aldoses by Benedict's or Fehling's reagents. [7] Copper ions react with an aldose to form a red precipitate, Cu 2 O. The reaction scheme of an aldose being oxidized by the copper ions in a Benedict's reagent solution. The R group provided is an example of a sugar backbone.
The number of open chain stereoisomers for an aldose monosaccharide is larger by one than that of a ketose monosaccharide of the same length. Every ketose will have 2 (n−3) stereoisomers where n > 2 is the number of carbons. Every aldose will have 2 (n−2) stereoisomers where n > 2 is the number of carbons. These are also referred to as ...
The best known ketose is fructose; it mostly exists as a cyclic hemiketal, which masks the ketone functional group. Fatty acid synthesis proceeds via ketones. Acetoacetate is an intermediate in the Krebs cycle which releases energy from sugars and carbohydrates.
In organic chemistry, Fehling's solution is a chemical reagent used to differentiate between water-soluble carbohydrate and ketone (>C=O) functional groups, and as a test for reducing sugars and non-reducing sugars, supplementary to the Tollens' reagent test. The test was developed by German chemist Hermann von Fehling in 1849. [1]