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The ketone group is the double-bonded oxygen. In organic chemistry, a ketose is a monosaccharide containing one ketone (>C=O) group per molecule. [1] [2] The simplest ketose is dihydroxyacetone ((CH 2 OH) 2 C=O), which has only three carbon atoms. It is the only ketose with no optical activity.
For many monosaccharides (including glucose), the cyclic forms predominate, in the solid state and in solutions, and therefore the same name commonly is used for the open- and closed-chain isomers. Thus, for example, the term "glucose" may signify glucofuranose, glucopyranose, the open-chain form, or a mixture of the three.
In organic chemistry, a ketone / ˈ k iː t oʊ n / is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)− (a carbon-oxygen double bond C=O). The simplest ketone is acetone (where R and R' is methyl), with the formula (CH 3) 2 CO ...
Fehling's test can be used as a generic test for monosaccharides and other reducing sugars (e.g., maltose). It will give a positive result for aldose monosaccharides (due to the oxidisable aldehyde group) but also for ketose monosaccharides, as they are converted to aldoses by the base in the reagent, and then give a positive result. [9]
Therefore, ketones like fructose are considered reducing sugars but it is the isomer containing an aldehyde group which is reducing since ketones cannot be oxidized without decomposition of the sugar. This type of isomerization is catalyzed by the base present in solutions which test for the presence of reducing sugars. [3]
They generally result from the nucleophilic addition of an alcohol (a compound with at least one hydroxy group) to an aldehyde (R−CH=O) or a ketone (R 2 C=O) under acidic conditions. The addition of an alcohol to a ketone is more commonly referred to as a hemiketal. Common examples of hemiacetals include cyclic monosaccharides.
Barfoed's test is a chemical test used for detecting the presence of monosaccharides. It is based on the reduction of copper(II) acetate to copper(I) oxide (Cu 2 O), which forms a brick-red precipitate. [1] [2] RCHO + 2Cu 2+ + 2H 2 O → RCOOH + Cu 2 O↓ + 4H + (Disaccharides may also react, but the reaction is much slower.)
Generally, Benedict's test detects the presence of aldehyde groups, alpha-hydroxy-ketones, and hemiacetals, including those that occur in certain ketoses. In example, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone which results to a positive test because the base component of Benedict converts it ...