What is The Difference between Ketone and Aldehyde?

Posted by Mike Miryala on


You must have heard of “aldehyde” and “ketone” and wonder if they mean the same thing? Well, there’s a clear-cut difference between these two carbonic chemical compounds, and we shall focus on that in this article.

Both ketones and aldehydes occur naturally and play important biological roles in metabolism. These two compounds also support many physiological processes. 

Beyond the human body, ketones and aldehydes have a wide range of commercial and industrial uses. They are often produced in mass and used industrially as reagents, solvents, and precursors to many products, such as different types of polymers.

While both ketone and aldehyde have a common carbonyl center within their chemical structure, there is a difference in the chemical arrangement of the surrounding atoms, and that’s the major difference between these two compounds.

Before moving further on their differences, let’s learn about ketones and aldehydes individually.


What is Ketone?



Ketones are characterized by the R-CO-R’ form, where one carbon atom forms a double bond with the oxygen atom. A ketone is never found at the end of a carbon chain as the carbonyl bond is surrounded by alkyl groups on both sides.

However, ketones are not as reactive as aldehydes. Nonetheless, they are widely used as industrial solvents in the form of acetone.

In terms of oxidation, a ketone is in the highest oxidation form and cannot be oxidized further. However, it can still undergo reduction reactions to form its corresponding alcohol.

A good way to recognize ketones is to check their IUPAC nomenclature. Their names always end with the suffix “one”. So, some common examples of ketones include hexanone, pentanone, butanone, etc.


What is Aldehyde?


An aldehyde has the chemical structure R-CHO, where the “C” atom forms a double bond with oxygen (R-(C=O)-H). Aldehyde groups are only positioned at the end of the carbon chain since an “H” atom is always found at the end of the chain. Hence, if a carbonyl group is found at the end of a chain, then it is an aldehyde.

Many industrial processes use aldehydes in the form of acetaldehyde and formaldehyde. In terms of reactivity, aldehydes are more reactive than ketones. Unlike ketones, aldehydes can be further oxidized to form carboxylic acids, and it can be reduced to form alcohols.

According to the IUPAC system of naming compounds, aldehydes always end with the suffix “al''. Hence, several aldehyde compounds include hexanal, butanal, propanal, etc. These are the aldehyde names of the respective alkyl groups.

Several laboratory grade tests, however, are used to distinguish ketones from aldehydes. These tests include the Fehling’s test, Tollen’s test, and Schiff’s test, among others.


So, what is the Difference Between Ketone and Aldehyde?



Looking at our brief overview above, you would have noticed some major differences between ketones and aldehydes. But let’s quickly summarize the differences based on important criteria.


  • Chemical structure: Ketones have the form of R-CO-R’ while Aldehydes have the form of R-CHO
  • IUPAC Nomenclature: Ketones end their names with the suffix “one” while Aldehydes end their names with “al”
  • Reactivity: Ketones cannot be further oxidized without breaking the carbon chain, but Aldehydes are more reactive and can undergo further oxidation to form carboxylic acids.
  • Natural occurrence: Ketones are naturally found in sugars and are called ketoses in general. Aldehydes are commonly found in volatile compounds such as fragrances.
  • Location of Carbonyl group: Ketones have their carbonyl group at the middle of the chain, while Aldehydes always have their carbonyl group at the end of a carbon chain.


What More on the Occurrence of Ketone and Aldehyde?


As mentioned earlier, ketones and aldehydes are widespread in nature.

Plants and microorganisms contain these chemical compounds as cinnamaldehyde (in cinnamon bark), Citra (in lemongrass), vanillin (in vanilla bean), carvone (in spearmint and caraway), helminthosporal (a fungal toxin), and camphor (in camphor trees).

In humans and animals, ketones are often found in form of progesterone (female sex hormone), testosterone (male sex hormone), muscone (musk deer), and cortisone (adrenal hormone). Ketones are also an alternative energy source for most organs of the human body, especially when the blood sugar level is low.


Which is Stronger - Ketone or Aldehyde?


The strength of the molecular bonds of a compound or substance is often related to its boiling and melting points. The dipole-dipole bonds between molecules of aldehydes are weaker compared to the molecular bond in ketones.

In other words, ketones are stronger than aldehydes. The boiling point of aldehydes is way lower than that of ketones, even with equal molecular weight. This is mainly attributed to the higher polarity of the ketone.


What are the Uses of Ketones and Aldehydes?


Ketones are used for several purposes. It is used industrially as a solvent. Acetone works as a paint thinner and nail paint remover.

However, ketones are widely used in medicine. Ketones serve as fuel to drive the body’s metabolism. It also works to support muscular function. Then insulin is often a solution when the body’s insulin level drops drastically.

On the other hand, aldehydes are used for different industrial and commercial purposes. 40% formaldehyde solution forms Formalin which is used in preserving biological specimens. 

This solution is also used in tanning, embalming, and preparing polymeric products and glues. It is also used as insecticides, germicides, and fungicides. Benzaldehyde is used in cosmetic products, perfumes, and dyes. It is also to add almond flavor to food products.


Final Remark


Ketones and aldehydes are both natural chemical compounds found in plants, animals, and humans.

The major difference between these two compounds is that the active association of ketones occurs in between molecules while the active group of aldehydes occurs mainly in the terminus.

Although both compounds are classified as carbonyl compounds, their structure and positioning of their functional groups influences their physical and chemical properties.

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