--- title: "Butanone | Organic Chemistry" description: "Butanone is a ketone with formula CH3COCH2CH3, used in Organic Chemistry to identify carbonyl structure, reactivity, and IR absorption." canonical: "https://fiveable.me/organic-chem/key-terms/butanone" type: "key-term" subject: "Organic Chemistry" unit: "Unit 20" --- # Butanone | Organic Chemistry ## Definition Butanone is a ketone, specifically CH3COCH2CH3, with a carbonyl group inside a four-carbon chain. In Organic Chemistry, it shows up as a basic carbonyl example and an IR-signature compound. ## What It Is Butanone is a ketone in Organic Chemistry, meaning it has a carbonyl group, C=O, bonded to two carbon atoms. Its structure is CH3COCH2CH3, so the carbonyl is in the middle of the chain, not at the end. You may also see it called methyl ethyl ketone, or MEK. That structure matters because ketones behave differently from aldehydes, carboxylic acids, and esters. In butanone, the carbonyl carbon is polarized, with the oxygen pulling electron density toward itself. That makes the C=O bond strongly polar and gives the molecule a noticeable dipole, which affects boiling point, solubility, and reaction patterns. Butanone is a good example of how functional groups control chemical behavior. Even though it has four carbons, the carbonyl group dominates the molecule’s chemistry. The alkyl groups on either side donate some electron density, but they do not erase the electrophilic character of the carbonyl carbon. So nucleophiles still tend to attack that carbon during carbonyl reactions. In lab and on exams, butanone often appears as a reference ketone because it is simple but not symmetric like acetone. That makes it useful for naming practice and structure recognition. If you see CH3COCH2CH3, you should identify the middle carbonyl and name the compound as butanone, not an aldehyde, because the carbonyl carbon is attached to two carbon groups, not one carbon and one hydrogen. It also comes up in spectroscopy. In an IR spectrum, butanone shows a strong, sharp C=O stretch around the usual ketone region, which makes it easier to spot a ketone than a compound that only has C-H or C-C bonds. Since it lacks the broad O-H band of acids or alcohols, the spectrum helps you separate it from related functional groups quickly. ## Why It Matters Butanone matters because it gives you a clean example of ketone behavior, and ketones are one of the core carbonyl families in Organic Chemistry. Once you can read butanone correctly, you can transfer that skill to many other molecules with C=O groups. It also connects structure to reactivity. The carbonyl carbon is electrophilic, so reactions often begin with nucleophilic attack there. That idea shows up again and again in carbonyl chemistry, whether you are comparing ketones to aldehydes or predicting what happens in reduction, addition, or condensation reactions. Butanone is especially useful for spectroscopy practice. The IR carbonyl stretch gives you a fast visual clue that a ketone is present, and the absence of O-H or N-H signals helps narrow the identity of the compound. In a structure ID problem, that combination of clues can save you a lot of guessing. It also helps with naming and drawing. If you can place the carbonyl in butanone correctly, you are practicing the same logic you need for other ketones and for more complex molecules with multiple functional groups. That makes it a small molecule with a big payoff in carbonyl recognition. ## Connections ### Ketone Butanone is a ketone, so this is the category that explains its structure and reactivity. The key idea is that the carbonyl carbon is attached to two carbon groups, which makes it different from an aldehyde. When you see butanone, you are seeing a specific example of ketone chemistry rather than a separate functional-group family. ### [Carbonyl Group](/organic-chem/key-terms/carbonyl-group) The carbonyl group is the part of butanone that drives most of its chemical behavior. The C=O bond is polar, so the carbonyl carbon is electrophilic and the oxygen is electron-rich. In naming, spectroscopy, and reaction prediction, the carbonyl is the feature you pay attention to first. ### Infrared Spectroscopy Butanone is easy to recognize in IR because ketones give a strong C=O stretching absorption. That peak helps you identify a carbonyl-containing compound even when the rest of the molecule is simple. In a spectrum question, you would use butanone to practice spotting the ketone signal and ruling out acids or nitriles. ### [Acetone](/organic-chem/key-terms/acetone) Acetone is another common ketone, and it is often compared with butanone because both have a carbonyl group in the middle of the molecule. The difference is in carbon count and structure, which affects naming and symmetry. Comparing the two helps you see how ketones can share the same functional group while still being distinct compounds. ## On the AP Exam A structure ID question may show you CH3COCH2CH3 or a line-angle drawing and ask for the name, functional group, or likely IR peak. You would identify the carbonyl, recognize that it is bonded to two carbons, and label the molecule as a ketone, specifically butanone. In an IR problem, you would look for the sharp carbonyl stretch as evidence for a ketone and use the missing O-H band to rule out acids or alcohols. In naming practice, butanone is also a quick check that you can place the carbonyl correctly in a four-carbon chain. If a problem asks how the molecule might react, you would focus on the electrophilic carbonyl carbon rather than the alkyl parts of the chain. ## Butanone vs Acetone Butanone and acetone are both ketones, so they are easy to mix up. Acetone has three carbons and is symmetrical, while butanone has four carbons and an unsymmetrical structure. If a question asks for the exact name or formula, count the carbon skeleton first instead of stopping at "ketone." ## Key Takeaways - Butanone is a ketone with the formula CH3COCH2CH3, so its carbonyl carbon sits in the middle of the chain. - The carbonyl group makes butanone polar and gives it the reactivity you expect from a ketone. - In IR spectroscopy, butanone shows a strong C=O stretch that helps you identify a ketone quickly. - Butanone is useful because it is a simple, clear example of how carbonyl structure affects naming, spectra, and reactions. - When you see butanone in a problem, check the carbonyl position first, then use that to decide the name, functional group, and likely behavior. ## FAQs ### What is butanone in Organic Chemistry? Butanone is a ketone with the formula CH3COCH2CH3. The carbonyl group is on the second carbon of a four-carbon chain, which makes it a simple example of ketone structure and naming. ### Is butanone an aldehyde or a ketone? It is a ketone, not an aldehyde. The carbonyl carbon in butanone is attached to two carbon groups, while an aldehyde has a carbonyl at the end of a chain with at least one hydrogen attached. ### What does butanone look like on an IR spectrum? Butanone shows a strong, sharp carbonyl stretch in the ketone region of the IR spectrum. Because it does not have an O-H group, you will not see the broad acid or alcohol band that would point to a different functional group. ### How do you name CH3COCH2CH3? Count the four-carbon chain and identify the carbonyl as part of a ketone. The correct name is butanone, and you may also see the common name methyl ethyl ketone. ## Related Study Guides - [20.8 Spectroscopy of Carboxylic Acids and Nitriles](/organic-chem/unit-20/spectroscopy-carboxylic-acids-nitriles/study-guide/JOBRyouxJdayKhJZ) - [3.1 Functional Groups](/organic-chem/unit-3/functional-groups/study-guide/vpLNhUJH0OVqwdOq) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/organic-chem/key-terms/butanone#resource","name":"Butanone | Organic Chemistry","url":"https://fiveable.me/organic-chem/key-terms/butanone","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/organic-chem/key-terms/butanone#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:23:39.422Z","isPartOf":{"@type":"Collection","name":"Organic Chemistry Key Terms","url":"https://fiveable.me/organic-chem/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/organic-chem/key-terms/butanone#term","name":"Butanone","description":"Butanone is a ketone, specifically CH3COCH2CH3, with a carbonyl group inside a four-carbon chain. 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