What is Aldose?
According to experts, aldose can be defined as a monosaccharide or simple sugar group that has a carbon backbone chain. The carbon backbone chain of aldose contains a carbonyl group on the last carbon atom of the chain. This makes the chain into an aldehyde. Further, hydroxyl groups are also connected to all the other carbon atoms of the compound.
The main difference between aldose and ketose lies in the fact that compounds belonging to the ketose group have a carbonyl group away from the end of the entire molecule. This is also one of the primary reasons why those compounds are called ketones.
What is Ketose?
On the other hand, a ketose is also a monosaccharide group that contains one ketone group on every molecule. The simplest type of ketose is dihydroxyacetone. This ketose has only three carbon atoms, and it is also a compound that shows no optical activity. It is important for readers to remember that all monosaccharide ketoses fall under the category of reducing sugars. This is because these compounds can tautomerize into aldoses. This is done through an aldol intermediate. Further, the final aldehyde group can also be oxidized. Some good examples of this reaction are Tollen’s test or Benedict’s test. Readers should also note that ketoses that are bound into glycosides are nonreducing sugars - for example, the case of fructose moiety of sucrose.
Aldose Vs Ketose
Till now, we have learned what aldose sugar and ketose sugar mean. Now, it is time to learn the difference between aldose and ketose. Let’s start looking at things from a very basic point.
Students must be familiar with the fact that ketose sugar and aldose sugar are both types of monosaccharides. These monosaccharides can be differentiated based on the group that they contain.
On the basis of this, aldose can be defined as a monosaccharide that contains a carbon skeleton with an aldehyde group. This group is usually found in plants. Ketose, on the other hand, is a type of monosaccharide that contains a carbon skeleton with a ketone group. In the presence of reducing sugar, this group can be isomerized to aldose.
Ketose is a group that is usually used in processed food items. Some examples of ketose include ribulose and fructose. If an individual wants to find the difference between aldose and ketose, then he or she can perform the Seliwanoff’s Test. After conducting this test, the colour of aldose will change to light pink, and the colour of ketose will change to a deep cherry red.
A table has also been formulated of all of those differences. And that table is mentioned below.
Fun Facts About Aldose and Ketose
Did you know that aldoses are commonly known by the names that are specific to one stereoisomer of the compound? This distinction is extremely important in the branch of Biochemistry as many systems can only use a single enantiomer of the carbohydrate and not others.
However, this does not mean that aldoses are not locked into any one conformation. Rather, these compounds do tend to fluctuate between various forms. Students might also be interested to learn that aldoses can tautomerize into ketoses in a dynamic process. This is done through an enol intermediate.
This entire procedure is reversible. This means that aldoses and ketoses can also be thought of as being in constant equilibrium with one another. However, one should never forget that aldehydes and ketones are almost always more stable than their corresponding enol forms.
This means that both aldo- and keto- forms usually predominate. This entire procedure, along with its enol intermediate, also allows stereoisomerization. This procedure can be accelerated to form the interconversion of isomers by using basic solutions.
Comparison of Aldose and Ketose
Aldose can be defined as a simple sugar or monosaccharide which has a backbone chain of carbon. This backbone chain of carbon of aldose has a carbonyl group on the last carbon atom of the backbone chain and this makes the chain an aldehyde. In addition, hydroxyl groups are connected to all carbon atoms present in the compound. The main point which we can consider to differentiate between ketose and aldose is that compounds belonging to the ketose group have a carbonyl group away from the entire molecule’s end. This is one of the main reasons why they are defined as ketones.
Ketose can be defined as a monosaccharide group that contains a ketone group on every molecule and the simplest form of ketose is dihydroxyacetone which has 3 carbon atoms and it is a compound that does not show any optical activity. It is important to note that all monosaccharides ketoses are under the same category of reducing sugars and the reason is that these compounds can tautomerase into aldoses i.e. there can be an exchange of protons and electrons but the carbon chain is the same. This process involves an aldol intermediate which further oxidizes the final aldehyde group. An example of this is Tollen’s test reaction and Benedict’s test. It should also be noted that ketoses that are bound into glycosides are non-reducing sugars e.g. fructose is a moiety of sucrose. Reducing sugars has its uses in the food processing industry as well.
FAQs on Difference Between Adose and Ketose for JEE Main 2024
1. How are almonds different from ketose?
Ketose and aldoses are monosaccharides that are differentiated based on the group which they contain. Aldoses are defined as those monosaccharides that have a carbon skeleton that has an aldehyde group. These are primarily found in plants. On the other hand, ketoses are monosaccharides that have a carbon skeleton that has a ketone group. In the presence of reducing sugar, these can isomerize to aldose. They are used in processing food as well. Some of the examples of ketose are fructose and ribulose. Seliwanoof’s test can be used to differentiate between ketose and aldose. In this, the colour of aldose changes to light pink and the colour of ketose changes into deep cherry red.
2. How are aldoses named?
Aldoses are differentiated by the number of carbons in the main carbon chain. The minimum carbons present in the backbone needed to form a molecule are considered a carbohydrate and the carbohydrates with three carbons are called trioses. There is only one aldo-triose which is called glyceraldehyde that has one chiral stereo-centre with two enantiomers that are the L-glyceraldehyde and D-glyceraldehyde. Some of the common aldoses are as follows:
Triose which has 3 carbons – glyceraldehyde
Tetroses which have 4 carbons- erythrose
Pentoses have 5 carbons- xylose, ribose
Hexoses have 6 carbons – glucose
The most widely discussed category of aldoses is the hexoses which have 6 carbons. They are aldohexoses that have common names like D-(+)- Allose and D-(+)-Alltrose.
3. What is the stereochemistry of aldose?
Aldoses are referred to by names specific to the stereoisomer of the compound. They are important in Biochemistry. Aldoses do not just have a single conformation but they can fluctuate between different forms. Aldoses can donate a proton or electron i.e. undergo the process of tautomerisation to form ketoses with an enol or enediol intermediate. This reaction is reversible and ketoses are stable form than the enol forms. This allows steroisomerisation. Cyclic aldoses show Haworth projections and the open-chain forms of aldoses have Fischer projections which give stereochemical information about the structures.
4. What is the chemical nature of ketoses?
Ketose is a monosaccharide that has one ketone group per molecule and the simplest form of this group is the dihydroxyacetone. This contains only 3 carbon atoms and thus do not show any optical activity properties. One must note that all the ketoses that are monosaccharides belong to the group of reducing sugars. This is because they can tautomerase into aldoses via an enediol or enol intermediate which results in an aldehyde that can be oxidised. For example, in Benedict’s test and Tollens’ test. Other ketoses that are bound to glycosides are non-reducing sugars. An example is the fructose moiety of sucrose.
5. What test can be done to differentiate the ketose and aldose?
Ketones and aldoses can be differentiated or distinguished chemically by performing Seliwanoff’s test in which a sample is heated with acid and resorcinol. The mechanism of the reaction is mainly based on dehydration reaction which occurs quicker in the ketoses than the aldoses. Aldoses react in a slow manner resulting in a light pink colour whereas; the ketoses which react quickly will produce a dark red colour. Ketoses can isomerise to aldoses by the Lobry-de Bruyn-van Ekenstein process.