Question

How does an aldehyde sugar differ from ketone sugar?

Answer 1

Sugars are the simple forms of monosaccharide. Aldehyde sugar also called Aldoses and ketose sugar also called ketoses are two subcategories of the monosaccharides. Aldose contains aldehyde groups in its structure, whereas ketoses contain ketone groups in their structures.

Complete step-by-step answer: An aldehyde sugar is a monosaccharide with carbon backbone and an aldehyde group attached with it.
A ketose sugar is a monosaccharide with carbon backbone and a ketone group attached with it.
The differences between both are as follows.

Aldehyde Sugar	Ketone sugar
1. It is a pure form of sugar	1. It is an impure form of sugar.
2. An aldehyde sugar is primarily found in plants. A classic example is that of glucose.	2. Ketose sugar can be found majorly in processed foods. For example: Fructose.
3. It contains an aldehyde group in its structure along with a carbon chain	3. It is a monosaccharide which contains ketone groups in its structure along with carbon chains.
4. An aldose may decompose into ketose depending on the isomerization reaction.	4. Ketoses can isomerize into aldoses only if the carbonyl group is at the end of the carbon.
5. Majority of them have cyclical structure. They mostly form six-membered ring structure referred to as hemiacetal ring	5. Some of the ketone sugars like fructose forms a five membered ring referred to as hemi-ketal
6. Examples: glucose, galactose, erythrose, glyceraldehyde	6. Examples: Fructose, ribulose, tagatose, sorbose, heptoses, xylulose etc.
7. The chemical formula of an aldehyde sugar can be written as ${{C}_{n}}{{\left( {{H}_{2}}O \right)}_{n}}$	7. The chemical formula of ketose is written as RCOR.

Note: It should be noted that there is a test called “Seliwanoff’s test” which is used to differentiate both. In this test both sugars are heated with resorcinol. Aldehyde sugar delivers a slow light pink color whereas ketone sugar delivers a deep cherry-red color.