Difference Between Aldose and Ketose (With Table)

Aldose and ketose are two types of sugar molecules. Ketose has a ketone as functional group, while Aldose has an aldehyde. Aldoses are monosaccharides containing an aldehyde group and can be further categorized into aldopentoses and aldohexoses. Ketoses are monosaccharides containing a ketone group and can be categorised into ketopentoses and ketohexoses.

Aldose vs Ketose

The main difference between aldose and ketose is that Aldose is distinguished from ketose by the presence of a single group of aldehyde (RCHO) with carbon atom chains. Ketose, on the other hand, only has one ketone group per molecule. Furthermore, glucose is an aldose molecule, whereas fructose is a ketose molecule.

In organic chemistry, an aldose (from the German Aldehyd, older name: saccharose) is a monosaccharide containing only one aldehyde functional group per molecule. The chemical formula of an aldose is Cn(H2O)n. Aldose refers to a sugar that has one aldehyde group per molecule in its acyclic form.

A Ketose is a monosaccharide (a monomer of a carbohydrate) containing a ketone functional group. They have the general formula Cn(H2O)n. Ketose sugars are named like other sugars, with -ose being the suffix, except that they are prefixed with keto- to indicate the presence of a ketone group. For example, fructose is a ketohexose (a 6-carbon sugar).

Comparison Table Between Aldose and Ketose

Parameters of ComparisonAldoseKetose
Formula for ChemicalsCn(H2O)n is the chemical formula for aldose.During the Seliwanoff test, the ketose turns a rich cherry red colour.
FormationGlycolaldehyde will be formed from the aldose.Dihydroxyacetone will be formed from the ketose.
It is present inPlants contain the aldose sugar molecule.Processed foods include the sugar molecule ketose.
It is made up ofAldose is made up of a single aldehyde group.Ketose is made up of just one ketone group.
The test of SeliwanoffWhen Seliwanoff’s test is conducted, the aldose turns bright pink.When the Seliwanoff test is performed, the ketose turns a rich cherry red colour.

What is Aldose?

Aldoses can be classified as either reducing sugars or nonreducing sugars depending on whether the carbonyl group is placed at the end (terminus) of the chain or not. The two main forms of aldoses are the linear form and the cyclic form, both consisting of carbon and oxygen with hydrogen atoms attached to them. They are named according to their chain length.

Thus, for example, CH2OHCH2OH is called glycolaldehyde, because it has two carbons and CHO is called formaldehyde. The simplest possible aldose is glycolaldehyde. The term is used in biochemistry and pharmacology, where it has the following properties:

Aldoses are reducing sugars. When they are oxidized, they form substances called aldonic acids. The most common aldoses are the monosaccharides glucose, fructose and galactose, which have the chemical formula C6H12O6.

Aldoses can exist either as open-chain or cyclic structures. The open-chain structure is an unbranched polyhydroxyaldehyde containing at least three carbon atoms.

The chemical structure of an aldose has the general form H–(CHOH)n–CHO.[2] In this notation the carbon atom at position 1 is labeled as the carbonyl (C=O), or aldehyde, group. Aldoses with more than three carbons can be classified by the number of carbons between the carbonyl group and the first asymmetric carbon atom (also known as the chiral center) as primary (1 carbon), secondary (2 carbons), or tertiary (more than 2 carbons). Aldoses are

What is Ketose?

Ketose sugars are an important class of monosaccharides. The term ketose refers to a sugar (such as fructose) that contains one ketone group per molecule in its acyclic form(e.g., not including the hydroxyl groups bonded directly to the carbons of the ring). The simplest ketoses are dihydroxyacetone and erythrulose, both trioses having three carbon atoms. The former is an important intermediate in carbohydrate metabolism. Ketoses can isomerize into aldoses by the mutarotation reaction.

The simplest ketose is dihydroxyacetone, which has only three carbon atoms: it exists in equilibrium with its enol tautomer (1,3-diketo-1,3-dihydroxy-2-butene). More complex ketoses may be named according to the IUPAC nomenclature of carbohydrates; for example, 2-ketohexose would be a hexose sugar with a ketone group on the second carbon atom.

Ketose sugars exist in equilibrium with their open chain form and their cyclic hemiacetal or hemiketal form. In plants and animals, they are produced when aldoses undergo reduction. They are also produced from certain reactions of amino acids, called transamination reactions, which create alpha-ketoacids that can then be converted to sugars. Ketosis is the result of excessive accumulation of ketone bodies in blood due to inadequate carbohydrate stores.

Main Differences Between Aldose and Ketose

  1. Aldose does not dehydrate as quickly as ketose during Seliwanoff’s test, which dehydrates three times faster.
  2. The aldehyde groups are found in aldose monosaccharides. Ketone groups, on the other hand, are present in ketose monosaccharides.
  3. During the Seliwanoff test, aldose interacts with Seliwanoff reagent and becomes pale pink. Ketose, on the other hand, turns a cherry red hue when it interacts with the reagent.
  4. Because aldose sugar is found in plants, it is healthier for humans than ketose sugar, which is found in harmful foods (soft drinks, candies, etc.)
  5. The process of isomerization can convert aldose sugar to ketose sugar. Furthermore, the same procedure may be used to convert ketose sugar to aldose sugar.

Conclusion

The fundamental distinction between Aldose and Ketose is that Aldose contains an aldehyde group, while ketones contain a ketone group. The differences between these two molecules are that aldehydes will always have the carbonyl carbon next to the last carbon of the chain, whereas ketones will have their carbonyl carbon not next to the end of the chain.

An example of an aldose sugar is glucose (C6H12O6) , which has six carbons and an aldehyde group at the beginning of its carbon chain. A ketose sugar is fructose (C6H12O6), which has six carbons and a ketone group at the beginning of its carbon chain.

References

  1. https://www.sciencedirect.com/science/article/pii/S0008621500846297
  2. https://pubs.rsc.org/en/content/articlehtml/2017/cy/c7cy00281e