Main Difference – Aldehyde vs Ketone
Both aldehydes and ketones are carbonic chemical compounds containing a carbonyl group. A carbonyl group contains a carbon atom which is doubly bonded to an oxygen atom (C=O). The main difference between Aldehyde and Ketone is their chemical structure; even though both aldehydes and ketones share a carbonyl centre within their chemical structure, their chemical arrangement of the surrounding atoms is different. While the carbonyl group of an aldehyde is bound to an alkyl group on one side and to an H atom on the other side, ketone’s carbonyl group is bound to two alkyl groups (can be same or different) on either side.
This article explores,
1. What is Aldehyde?
– Structure, Naming, Properties, Tests
2. What is Ketone?
– Structure, Naming, Properties
3. What is the difference between Aldehyde and Ketone?
What is Aldehyde
As mentioned above, an aldehyde’s chemical structure can be defined as R-CHO, where the C atom is doubly bonded to the oxygen (R-(C=O)-H). Since one end of an aldehyde is always an H atom, aldehyde groups can only be found at the end of a carbon chain. Therefore, if a carbonyl group is found at the end of a carbon chain, it is definitely an aldehyde. Aldehydes are extremely useful chemical compounds in industry. i.e. formaldehyde and acetaldehyde
Aldehydes are more reactive when comparing with ketones. It can be reduced to form alcohols and also can be further oxidised until it forms carboxylic acids. Other numerous reactions follow depending on the nature of the carbon chain the aldehyde is attached to. When naming aldehydes according to the IUPAC system, it ends with a suffix ‘al’. Therefore, names such as propanal, butanal, hexanal, etc. are the aldehydes of the respective alkyl groups. An aldehyde can be distinguished from a ketone through several laboratory grade tests. The Schiff’s test, Tollen’s test, Fehling’s test are among the popular tests. For example, in the Fehling’s test, the aldehydes form a red precipitate whereas ketones do not show a reaction.
What is Ketone
The chemical structure of ketones is characterised by the R-CO-R’ form, where the C atom is doubly bonded to the oxygen atom. As the carbonyl bond is surrounded by alkyl groups on either side, a ketone will never be found at the end of a carbon chain.
Ketones are not as reactive as aldehydes. However, they are often used as industrial solvents. i.e. acetone. Ketones are in its highest oxidation form and therefore cannot be oxidised further. However, it readily undergoes reduction reactions forming the corresponding alcohol. Ketones can be easily recognised by their IUPAC name which ends with a suffix, ‘one’. For example, butanone, pentanone, hexanone, etc.
Difference Between Aldehyde and Ketone
Chemical Structure
Aldehydes have the form of R-CHO.
ketones have the form of R-CO-R’.
Reactivity
Aldehydes are more reactive than ketones. Aldehydes undergo oxidation forming carboxylic acids.
Ketones cannot be oxidised without breaking the carbon chain.
IUPAC Nomenclature
Aldehydes end with the suffix ‘al’
Ketones end with the suffix ‘one’.
Location of Carbonyl Group
Aldehydes always occur at the end of a carbon chain.
Ketones always occur at the middle of the chain.
Natural Occurrence
Aldehydes are usually found in volatile compounds such as fragrance compounds.
Ketones are commonly found in sugars and are referred to as ketoses in general. However, there are aldehyde sugars which are called aldoses. (Read the Difference Between Aldose and Ketose)
Image Courtesy:
“Aldehyde_Structural_Formulae” By Jü – Own work (Public Domain) via Commons Wikimedia
“Ketone-general” By Benjah-bmm27 (based on copyright claims). Own work assumed (Public Domain) via Commons Wikimedia
