--- title: "Alkyne | Organic Chemistry" description: "Alkyne is a hydrocarbon with a carbon-carbon triple bond, shaping naming, unsaturation, and reactions in Organic Chemistry." canonical: "https://fiveable.me/organic-chem/key-terms/alkyne" type: "key-term" subject: "Organic Chemistry" unit: "Unit 1" --- # Alkyne | Organic Chemistry ## Definition An alkyne is an organic compound with at least one carbon-carbon triple bond (C≡C). In Organic Chemistry, alkynes are a core unsaturated functional group used in naming, mechanism, and synthesis. ## What It Is An alkyne is a hydrocarbon in Organic Chemistry that contains at least one carbon-carbon triple bond, written as C≡C. That triple bond is the whole reason alkynes behave differently from alkanes and alkenes: it makes the molecule unsaturated and gives it two pi bonds that can react. The simplest alkyne is acetylene, also called ethyne, which has the formula C2H2. Each carbon in the triple bond is sp hybridized, so the atoms around that bond line up in a straight line with a 180° bond angle. That linear shape is not just a drawing detail, it comes from the way the orbitals overlap to make the sigma bond and the two pi bonds. Because alkynes have fewer hydrogens than the matching alkane, they increase a molecule’s degree of unsaturation. If you are given a molecular formula and the DU is 2, an alkyne is one possible reason, since one triple bond counts as two degrees of unsaturation. That is why alkynes often show up when you are working backward from a formula to a structure. Naming an alkyne also follows a specific pattern. You use the suffix -yne, choose the longest chain that contains the triple bond, and number the chain so the triple bond gets the lowest possible number. For example, but-1-yne tells you the triple bond starts at carbon 1. In reactions, the triple bond is a useful handle for making and changing molecules. Alkynes can be formed by elimination from dihalides, and they can also undergo addition reactions, reduction, or oxidative cleavage. So when you see an alkyne in a problem, think of it as both a structural feature and a reaction site, not just a name ending. ## Why It Matters Alkynes show up anywhere you need to connect structure to reactivity in Organic Chemistry. The triple bond tells you a molecule is unsaturated, affects how you count degrees of unsaturation, and points you toward the right set of reactions. This term also helps you translate between naming and mechanism. If a molecule is called a terminal alkyne, you already know where the triple bond sits, how to number the chain, and what kinds of reactions are possible at that end of the molecule. That makes alkyne problems feel much less random. Alkynes matter in synthesis too. You can build them from dihalides through elimination, then use the alkyne as a stepping stone to an alkene, an alkane, or cleavage products depending on the reagents. That makes them a common intermediate in multistep reaction planning. The structure of the triple bond also explains why the compound is linear and why sp hybridization appears in the course. So this one term connects functional groups, orbital geometry, nomenclature, unsaturation, and reaction strategy all at once. ## Connections ### sp Hybridization The carbon atoms in a triple bond are sp hybridized, which explains the linear shape of alkynes. Each carbon uses two sp orbitals for sigma bonds, while the leftover p orbitals form the two pi bonds. If you can picture that orbital setup, the geometry of an alkyne makes a lot more sense. ### Unsaturated Compounds Alkynes are one type of unsaturated compound because they contain pi bonds instead of only single bonds. That matters when you calculate degree of unsaturation from a formula or compare alkynes to alkanes and alkenes. The triple bond makes the molecule less hydrogen-rich than a saturated hydrocarbon. ### Organic Synthesis In synthesis, an alkyne is often a useful intermediate rather than the final target. You can form it by elimination from a dihalide, then convert it into other functional groups through addition, reduction, or cleavage. That makes alkynes a good place to think about choosing reagents with a goal in mind. ### [-ene](/organic-chem/key-terms/ene) Alkynes and alkenes are easy to mix up because both are unsaturated hydrocarbons, but the suffix tells you the bond type. -ene means a carbon-carbon double bond, while -yne means a carbon-carbon triple bond. The extra pi bond changes geometry, reactivity, and naming rules. ## On the AP Exam A quiz item or problem set usually asks you to do one of three things with an alkyne: name it, identify it from a structure, or use it in a reaction sequence. You might need to number the parent chain correctly, recognize a terminal versus internal triple bond, or count the degree of unsaturation from a molecular formula. In mechanism questions, you may be asked why an alkyne is linear, why it reacts with electrophiles, or how it can be made from a dihalide through elimination. In synthesis problems, the move is usually to choose the right reagent set to stop at an alkene, fully reduce to an alkane, or cleave the triple bond into carbonyl products. When you see C≡C, treat it as both a naming clue and a reaction clue. ## Alkyne vs -ene Alkynes and alkenes both contain multiple bonds, but they are not the same functional group. An alkene has a C=C double bond, while an alkyne has a C≡C triple bond. That extra bond changes the suffix in the name, the number of pi bonds, and the kinds of reactions the molecule can undergo. ## Key Takeaways - An alkyne is an unsaturated hydrocarbon with at least one carbon-carbon triple bond. - The triple bond makes the two carbons sp hybridized and gives the molecule a linear shape. - One triple bond counts as two degrees of unsaturation, so alkynes matter when you work from a molecular formula to a structure. - Alkynes are named with the suffix -yne, and the triple bond gets the lowest possible number in the parent chain. - In synthesis, alkynes are useful because they can be formed by elimination and then transformed by addition, reduction, or cleavage. ## FAQs ### What is an alkyne in Organic Chemistry? An alkyne is a hydrocarbon that contains at least one carbon-carbon triple bond, written C≡C. In Organic Chemistry, that triple bond makes the molecule unsaturated and gives it a linear shape at the bonded carbons. Alkynes are common in naming, degree of unsaturation problems, and reaction sequences. ### How do you tell an alkyne from an alkene? Look at the bond between the carbons. An alkene has a double bond, C=C, while an alkyne has a triple bond, C≡C. The name changes too, with -ene for alkenes and -yne for alkynes. That difference changes geometry and reactivity, so it is worth spotting fast. ### Why does an alkyne count as unsaturated? Because it contains pi bonds instead of only single bonds. Compared with the matching alkane, an alkyne has fewer hydrogens and can still react by adding atoms across the triple bond. In degree of unsaturation problems, one triple bond counts as two units of unsaturation. ### How are alkynes made in Organic Chemistry? A common preparation is double elimination from a vicinal or geminal dihalide, usually with a strong base. That process removes two equivalents of HX and builds the triple bond. In synthesis questions, this is the standard way to convert a saturated starting material into an alkyne. ## Related Study Guides - [1.9 sp Hybrid Orbitals and the Structure of Acetylene](/organic-chem/unit-1/sp-hybrid-orbitals-structure-acetylene/study-guide/3BISoNiqLEyPh9Cc) - [9.1 Naming Alkynes](/organic-chem/unit-9/naming-alkynes/study-guide/ILmhHCUqBdQ4iKxp) - [9.6 Oxidative Cleavage of Alkynes](/organic-chem/unit-9/oxidative-cleavage-alkynes/study-guide/KuAikjfXW5y321dA) - [7.2 Calculating the Degree of Unsaturation](/organic-chem/unit-7/calculating-degree-unsaturation/study-guide/LyaMv3ZavQZL1xKx) - [9.5 Reduction of Alkynes](/organic-chem/unit-9/reduction-alkynes/study-guide/QkDQvsHx5qfrnTq7) - [10.8 Oxidation and Reduction in Organic Chemistry](/organic-chem/unit-10/oxidation-reduction-organic-chemistry/study-guide/ZAx29nian8zVxOgs) - [9.2 Preparation of Alkynes: Elimination Reactions of Dihalides](/organic-chem/unit-9/preparation-alkynes-elimination-reactions-dihalides/study-guide/eTVpmQNapc1PVorZ) - [9.3 Reactions of Alkynes: Addition of HX and X2](/organic-chem/unit-9/reactions-alkynes-addition-hx-x2/study-guide/rx7N99MoZMz3xBBY) - [3.1 Functional Groups](/organic-chem/unit-3/functional-groups/study-guide/vpLNhUJH0OVqwdOq) - [9.9 An Introduction to Organic Synthesis](/organic-chem/unit-9/introduction-organic-synthesis/study-guide/zWSWt45h5E3taPuq) ## 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/alkyne#resource","name":"Alkyne | Organic Chemistry","url":"https://fiveable.me/organic-chem/key-terms/alkyne","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/organic-chem/key-terms/alkyne#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"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/organic-chem/key-terms/alkyne#term","name":"Alkyne","description":"An alkyne is an organic compound with at least one carbon-carbon triple bond (C≡C). 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