--- title: "Ethyl Radical | Organic Chemistry" description: "Ethyl radical is a carbon-centered radical, C2H5•, formed by homolytic bond cleavage and used to compare radical stability in Organic Chemistry." canonical: "https://fiveable.me/organic-chem/key-terms/ethyl-radical" type: "key-term" subject: "Organic Chemistry" unit: "Unit 10" --- # Ethyl Radical | Organic Chemistry ## Definition The ethyl radical is C2H5•, a carbon-centered radical with one unpaired electron. In Organic Chemistry, it shows up as a simple, unstable radical used to compare against more stabilized radicals like allyl. ## What It Is The ethyl radical is a two-carbon radical, written as C2H5•, with one unpaired electron on carbon. In Organic Chemistry, you usually meet it as a simple example of a localized radical, meaning the electron is stuck on one carbon instead of being spread out. It can form by homolytic cleavage, where a C-H bond breaks evenly and each atom takes one electron from the bond. If ethane loses a hydrogen atom in that way, you get an ethyl radical. That makes it a good model for seeing what radicals are and how they form, even if it is not the most common species you will track in a reaction mechanism. What makes the ethyl radical useful is what it lacks. There is no adjacent pi system, no resonance path, and no special orbital setup that can delocalize the unpaired electron. Because of that, the radical stays relatively high in energy and reacts quickly. Organic Chemistry uses this kind of example to show that radical stability is not just about having an unpaired electron, but about where that electron can go. You can think of the ethyl radical as sitting near the low end of the radical-stability ladder. It is more stable than a methyl radical because it has one extra alkyl group nearby, which can donate some electron density through hyperconjugation. But it is still much less stable than an allyl radical, where resonance spreads the unpaired electron over three carbons. That contrast is the whole point. When you compare the ethyl radical to allyl or benzyl radicals, you can see how resonance and conjugation lower radical energy. The ethyl radical gives you the baseline case: a localized, reactive radical with no resonance stabilization, useful for ranking stability and predicting which radical intermediate is more likely to form or persist. ## Why It Matters The ethyl radical matters because Organic Chemistry is full of stability comparisons, and radicals do not all behave the same way. If you can recognize that C2H5• is a localized, poorly stabilized radical, you can predict that it will be short-lived and very reactive. This shows up when you compare different radical intermediates in reaction mechanisms. A question might ask which radical is more stable, or which pathway is more favorable, and the ethyl radical gives you a simple reference point. It also helps you separate resonance effects from weaker effects like hyperconjugation. The ethyl radical has some stabilization from its alkyl group, but not enough to compete with a resonance-stabilized radical like allyl. It also helps with arrow-pushing logic in radical chemistry. If a radical can move into a conjugated system, that usually changes both its stability and its reactivity. If it cannot, like the ethyl radical, it stays localized and reacts at the carbon holding the unpaired electron. That difference shows up in product prediction, intermediate ranking, and explanation questions about why one radical forms faster than another. ## Connections ### Allyl Radical The allyl radical is the comparison point that makes the ethyl radical easy to judge. Allyl has resonance, so its unpaired electron is spread across three carbons, while the ethyl radical keeps the electron on one carbon. That difference is why allyl is much more stable and why resonance beats simple alkyl substitution. ### Resonance Resonance explains why some radicals are stabilized by delocalization and others are not. The ethyl radical has no adjacent pi system, so you cannot draw meaningful resonance structures for it. When you see resonance in a radical problem, you should immediately ask whether the unpaired electron can be spread out or must stay localized. ### Radical Stability Ethyl radical is a basic reference point for radical stability rankings. It is more stable than methyl, but less stable than allyl, benzyl, and many radicals supported by resonance. Comparing ethyl to other radicals helps you use the stability trends instead of memorizing isolated examples. ### [Hyperconjugation](/organic-chem/key-terms/hyperconjugation) Hyperconjugation gives the ethyl radical a small amount of stabilization from nearby C-H and C-C bonds. That effect is much weaker than resonance, but it explains why an ethyl radical is slightly more stable than a methyl radical. This comparison often comes up when you are ranking simple alkyl radicals. ## On the AP Exam A mechanism question might ask you to rank radicals, choose the more stable intermediate, or explain why one radical reacts faster than another. That is where the ethyl radical becomes a reference point: you identify it as a localized alkyl radical with no resonance stabilization, then compare it to allyl, benzyl, methyl, or other simple radicals. In problem sets, you may also be asked to draw the radical after a homolytic cleavage step, especially when a bond breaks evenly and each atom gets one electron. If a product or intermediate contains C2H5•, you should recognize that the radical center is on carbon and that there are no valid resonance forms to spread the unpaired electron. For short-answer or discussion questions, the move is usually to explain stability in terms of structure. Say whether the radical is stabilized by hyperconjugation only or by resonance as well, then use that to justify reactivity or product formation. ## Ethyl Radical vs Allyl Radical These get mixed up because both are carbon-centered radicals, but they are not stabilized the same way. The ethyl radical is localized on one carbon and has no resonance, while the allyl radical is delocalized across a three-carbon pi system. If you are asked which one is more stable, allyl wins by a lot. ## Key Takeaways - The ethyl radical is C2H5•, a carbon-centered radical with one unpaired electron on the ethyl group. - It forms by homolytic bond cleavage, so the radical comes from an even split of electrons in a bond-breaking step. - Unlike allyl or benzyl radicals, the ethyl radical has no resonance stabilization, so it stays localized and very reactive. - It is a useful baseline for radical stability because it sits near the simple alkyl end of the comparison scale. - You use it to explain why resonance and conjugation make some radicals much more stable than ordinary alkyl radicals. ## FAQs ### What is ethyl radical in Organic Chemistry? The ethyl radical is C2H5•, a two-carbon species with one unpaired electron. In Organic Chemistry, it is a simple carbon-centered radical used to study radical formation and stability. Because it has no resonance, it is much less stabilized than radicals like allyl. ### How is the ethyl radical formed? It forms by homolytic cleavage of a C-H bond, often described as removing a hydrogen atom from ethane. In that kind of bond-breaking, each atom keeps one electron from the bond. The result is a radical on carbon rather than a charged species. ### Is the ethyl radical stabilized by resonance? No, the ethyl radical does not have resonance stabilization because there is no adjacent pi system to delocalize the unpaired electron. You may still see it treated as a little more stable than methyl because of hyperconjugation, but that effect is much weaker than resonance. ### How does ethyl radical compare with allyl radical? Ethyl radical is localized, while allyl radical is delocalized across a conjugated three-carbon system. That delocalization makes allyl much more stable. If a question asks you to rank them, allyl is the more stable radical by a wide margin. ## Related Study Guides - [10.4 Stability of the Allyl Radical: Resonance Revisited](/organic-chem/unit-10/stability-allyl-radical-resonance-revisited/study-guide/MFgO0zOCxgMhT6rY) ## 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/ethyl-radical#resource","name":"Ethyl Radical | Organic Chemistry","url":"https://fiveable.me/organic-chem/key-terms/ethyl-radical","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/organic-chem/key-terms/ethyl-radical#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:23:40.731Z","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/ethyl-radical#term","name":"Ethyl Radical","description":"The ethyl radical is C2H5•, a carbon-centered radical with one unpaired electron. 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