Ketone
Organic compounds with a carbonyl group bonded to two carbons.
A ketone is an organic compound with the structure R−C(=O)−R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group −C(=O)−, a carbon-oxygen double bond. Many ketones are of great importance in biology and industry, including sugars (ketoses), steroids such as testosterone, and the solvent acetone.
- field
- Organic chemistry
- known_for
- Carbonyl group bonded to two carbon atoms; key functional group in biology and industry
- simplest_example
- Acetone ((CH3)2CO)
- nomenclature_origin
- Derived from Aketon, an old German word for acetone
Lore & Background
The word ketone is derived from Aketon, an old German word for acetone. According to IUPAC nomenclature, ketone names are derived by changing the suffix -ane of the parent alkane to -anone. The simplest ketone is acetone, where R and R' are methyl. Ketones are classified into symmetrical and unsymmetrical derivatives; acetone and benzophenone are symmetrical, while acetophenone is unsymmetrical. Many kinds of diketones are known, such as diacetyl, once used as butter-flavoring in popcorn. Cyclic ketones include cyclohexanone, an intermediate in nylon production, and muscone, an animal pheromone.
Reader's Guide
Ketones are distinguished from aldehydes by the carbonyl group being bonded to two carbons rather than one carbon and one hydrogen. This structural difference makes ketones more resistant to oxidation than aldehydes. The carbonyl group is polar, making ketones nucleophilic at oxygen and electrophilic at carbon. Ketones are hydrogen-bond acceptors but not donors, contributing to their volatility and use in perfumery and as solvents. Industrially, ketones are often produced by oxidation of hydrocarbons with air; for example, cyclohexanone is produced by aerobic oxidation of cyclohexane. Many synthetic methods exist, including oxidation of secondary alcohols, hydration of alkynes, and Friedel–Crafts acylation. Ketones give positive results in Brady's test and the iodoform test for methyl ketones, but negative results with Tollens' reagent, distinguishing them from aldehydes.
Did You Know?
- The simplest ketone is acetone, with the formula (CH3)2CO.
- Ketones are hydrogen-bond acceptors but not hydrogen-bond donors.
- Cyclohexanone, a cyclic ketone, is an important intermediate in the production of nylon.
- Ketones give positive results in Brady's test with 2,4-dinitrophenylhydrazine.
Frequently Asked Questions
What exactly defines a ketone in organic chemistry?
A ketone is an organic molecule whose core is a carbonyl group (a carbon double-bonded to oxygen) with that carbonyl carbon attached to two other carbon-containing groups, written R−C(=O)−R'. That two-carbon substitution on the carbonyl is the defining feature that separates ketones from aldehydes.
What's the simplest example of a ketone?
Acetone, (CH₃)₂CO, is the most basic ketone you'll meet—just two methyl groups flanking a central carbonyl carbon. It's the familiar nail-polish-remover solvent and the very compound that gave the entire class its name.
Where do ketones show up in biology and industry?
In biology, the ketone backbone appears in essential molecules like the steroid hormone testosterone and in ketose sugars such as fructose. In industry, acetone and related ketones serve as widely used organic solvents.
How is a ketone structurally different from an aldehyde?
The distinction lies in what neighbors the carbonyl carbon: a ketone has carbon groups on both sides, whereas an aldehyde has at least one hydrogen attached to that same carbon. That single substitution change noticeably shifts the molecule's reactivity and chemical behavior.
Why is the whole class called 'ketone'?
The term traces back to 'Aketon,' an older German word that originally referred specifically to acetone. Once chemists recognized that acetone was just one member of a broader family sharing the R−C(=O)−R' backbone, the name was generalized to cover all such compounds.
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