Difference Between Adose and Ketose

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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.

Difference Between Aldose and 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.








Mainly in plants

In processed food items


Isomerize into ketose

Isomerize into aldoses. This is done only in the presence of reducing sugar

Colour of Seliwanoff’s Test

Light pink

Deep cherry red


Glucose, ribose, and galactose

Fructose, ribulose, and erythrulose

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.

FAQ (Frequently Asked Questions)

1. What is the meaning of Aldotriose?

Answer: Aldotriose can be defined as a monosaccharide that contains an aldehyde or aldose group and three carbons or a triose. This word can be broken down to help understand the molecules that are a part of this group. The simplest aldotriose is glyceraldehyde.

Students might also be interested to learn about the concept of ketotrioses. Ketotrioses is a group of monosaccharides that contains both a ketone or ketose and a triose or collection of three carbonds. An example of ketotriose is dihydroxyacetone.

2. What is the class or group of chemical compounds that cannot be hydrolyzed into Aldose and Ketose groups?

Answer: Monosaccharides are the simplest group of carbohydrates. Monosaccharides cannot be hydrolyzed into any smaller molecules.

3. What do you understand by the Carbohydrates called glucose?

Answer: In most cases, carbohydrates have been given rather non-systematic names. However, the suffix ‘ose’ is usually used. And glucose is the most common carbohydrate. The chemical formula for glucose is C6H12O6. Glucose is also classified as a monosaccharide, an aldohexose, and reduces sugar. Further, some simple chemical reactions were used to establish the general structure of glucose and many other aldohexoses. An image depicting the structure of glucose is attached below.

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4. Write a short note on what you understand by the meaning of Aldose and Ketose.

Answer: An aldose is a group of compounds that are a type of carbohydrates which contain an aldehydic group. This group is represented by the -CHO formula. Aldose, as a group, can further be differentiated into many other groups based on the total number of carbon atoms in the chain.

Three carbon atoms are called aldotriose, four carbon atoms are called aldotetrose, five carbon atoms are called aldopentose, and six carbon atoms are called aldohexose. An example of this group is glucose.

On the other hand, a ketose is a group of carbohydrates that contain a keto or =CO group. This group can further be classified into other groups on the basis of the total number of carbon atoms present in the chain.

Three carbon atoms are called ketotriose, four carbon atoms are called ketotetrose, five carbon atoms are called ketopentose, and six carbon atoms are called ketohexose. An example of ketose is fructose.