In this tutorial, you will learn about the ketone functional group, how to name it, its properties, and its reactions. You will also learn about ketones compared to other similar functional groups.
Topics Covered in Other Articles
- Carbonyl Functional Group
- Aldol Condensation Reaction
- Keto Enol Tautomerization
- Diels-Alder Reaction
- Fischer Esterification
What is a Ketone?
Ketones are a common functional group in organic chemistry. Ketones have important physiological properties. As a result, they are a part of several sugars and compounds involved in medicinal use such as cortisone, an anti-inflammatory.
One common ketone is acetone (CH3COCH3). Acetone is soluble in water and can dissolve many organic compounds. It has a low boiling point of 56℃ which allows it to be removed from reactions by evaporation. It is commonly involved in industrial solvents such as paint strippers and nail-polish removers.
Ketones have a carbonyl group where the carbon is covalently double bonded to an oxygen atom. The other two bonds are either to other carbon atoms or hydrocarbon radicals. R1 and R2 denote identical or different carbon chains.
Due to its structure, the most basic molecular formula of a ketone is RCOR. This can be referred to as a Keto group as the -CO- group is attached to carbon atoms on both sides.
Carbonyl vs. Ketone
It is important to note the difference between carbonyl and ketone. The difference is that carbonyl groups have a carbon atom with a double-bonded oxygen atom, while ketones contain a carbonyl group attached to alkyl groups. The main takeaway is that carbonyl groups are a part of ketones, not the other way around
When naming ketones based on IUPAC rules, the longest carbon chain containing the carbonyl group is the parent. As a result, this chain is numbered in the direction that gives the carbonyl group the smallest number. The suffix of “-e” from the parent alkane is changed to “-one”. Several examples of ketones are shown below.
Aldehydes vs. Ketone
Aldehydes and ketones have a similar chemical composition and molecular structure. They both have a carbonyl functional group. The only difference is the atoms on the carbonyl carbon.
Aldehydes have an R group on one side of the carbonyl and a Hydrogen atom on the other. The R group in an aldehyde can either be a hydrocarbon chain or a Hydrogen. By contrast, ketones have R and R’ substituents attached to the carbonyl carbon. In addition to structure, there are five notable differences.
- Generic forms: Aldehydes have the R-CHO generic form, while ketones have the R-CO-R’ generic form.
- Chemical reactivity: Aldehydes are more chemically reactive than ketones. Ketones cannot be easily oxidized without breaking the carbon chain.
- Carbonyl location: The aldehyde functional group is located at the end of the carbon chain due to the hydrogen attachment. However, the ketone functional group is always located in the middle of the carbon chain.
- Typical occurrence: Aldehydes are found with volatile compounds, whereas ketones are found in sugars.
- IUPAC nomenclature: The nomenclature of aldehydes uses the suffix “-al” while ketones use the suffix “-one”.
Reactions of Ketones
Ketones are able to undergo many different types of reactions. The list below names the most common reactions which they can undergo.
Nucleophilic Addition Reaction
Ketones utilize nucleophilic addition reactions where the electron-rich nucleophile attacks the electron-deficient electrophiles. In ketones, the carbon atom within the carbonyl acts as the electrophile.
Addition of Cyanide
Ketones react with HCN (hydrogen cyanide) to produce cyanohydrins. As a result, the CN– (strong nucleophile) adds to the carbonyl compound to yield a cyanohydrin.
Addition of Grignard Reagents
Ketones also react with Grignard reagents to form alcohols. The Grignard reagent adds to the carbonyl group using nucleophilic addition. As a result, this produces an adduct which then creates an alcohol. The reaction with ketones yields tertiary alcohol.
Ketones can go through reduction where there is a loss of oxygen and a gain of hydrogen.
Reduction to Alcohols
Ketones reduce to their corresponding alcohols through catalytic hydrogenation. The addition of hydrogen either takes place in the presence of catalysts (platinum, nickel) or in sodium borohydride (NaBH4). In this process, ketones yield secondary alcohols.
Wolff-Kishner Reduction Reaction
In Wolff-Kishner reduction, the carbonyl group in a ketone reduces to a CH2 group. To learn about this reaction in further detail, read the Wolff-Kishner Reduction Reaction article.
Ketones can undergo oxidation reactions but require strong oxidizing agents and elevated temperatures. The oxidation consists of carbon-carbon bond cleavage and forming a carboxylic acid.
Aldol Condensation Reaction
Ketones are able to undergo Aldol Condensation Reactions.