Alkyne Reactivity
Alkyne Reactivity - Related Videos
02:39
Nomenclature of Alkynes
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2025
Alkynes are unsaturated hydrocarbons characterized by the presence of carbon-carbon triple bonds and have a general formula CnH2n-2. The nomenclature of alkynes follows a set of rules similar to alkanes and alkenes; however, alkynes bear the suffix "-yne" instead of "-ane" or "-ene." There are two approaches to naming alkynes: • IUPAC names • Common names IUPAC nomenclature The IUPAC naming system follows a systematic approach to deduce names of alkynes based on their chemical structure.
02:42
Acidity of 1-Alkynes
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2023
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here. Ethane (pKa = 51) Ethene (pKa = 44)
02:34
Preparation of Alkynes: Dehydrohalogenation
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2025
Introduction Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions. Reaction Mechanism – E2 pathway Vicinal dihalides In the first elimination step, the strong base abstracts the proton from the dihalide that is oriented anti to the leaving group. Since E2 reactions follow a...
09:08
Detecting Reactive Oxygen Species
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2023
Reactive oxygen species are chemically active, oxygen-derived molecules capable of oxidizing other molecules. Because of their reactive nature, there are many deleterious effects associated with unchecked ROS production, including structural damage to DNA and other biological molecules. However, ROS can also be mediators of physiological signaling. There is accumulating evidence that ROS play significant roles in everything from activation of transcription factors to the mediation of...
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Mass Spectrometry: Alkyne Fragmentation
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2024
The fragmentation of alkynes preferentially occurs at the carbon–carbon bond between the α and β carbon of the alkyne bond to generate a 3-propynyl cation (or propargyl cation). In terminal alkynes, there is the only type of fragmentation that yields the 3-propynyl cation. The unsubstituted 3-propynyl cation exhibits a peak at a mass-to-charge ratio of 39. In internal alkynes, the 3-propynyl cation is substituted. For example, 2-pentyne fragments into methyl-substituted 3-propynyl cation, which...
FAQs
The polarized π bonds in an alkyne influence how electrophilic reagents approach the triple bond, while its linear geometry shapes the reactive arrangement. Consequently, electrophilic addition provides a direct route for converting the unsaturated group into new functionalized products. This combination of polarization and geometry explains why alkynes serve as versatile starting points in reaction design.
Terminal alkynes can be converted into acetylide nucleophiles by deprotonation, giving the molecule a carbon-centered reaction site. That nucleophilic form enables carbon–carbon bond formation, unlike simply modifying the existing triple bond through addition. In synthesis, this pathway is useful when the objective is to connect an alkyne-containing fragment to another carbon framework and build a substituted alkyne.
Catalytic hydrogenation can reduce an alkyne selectively or completely, so the extent of reduction becomes a key product-control variable. Selective reduction provides an alkene, whereas complete reduction removes the unsaturation more extensively. This choice allows chemists to retain or eliminate the triple-bond-derived unsaturation according to the functional-group transformation required.
Electrophilic addition introduces new functionality through reaction with hydrogen halides, halogens, or water, whereas catalytic hydrogenation focuses on reducing the carbon–carbon multiple bond. The first strategy helps access functionalized products, including carbonyl compounds, while the second can provide alkenes or more completely reduced products. Distinguishing these pathways helps align reagent choice with the intended synthetic outcome.
A useful planning sequence begins by identifying whether the substrate is a terminal alkyne, because that determines whether deprotonation can generate an acetylide nucleophile for carbon–carbon bond formation. The chemist can then select electrophilic addition to introduce functionality, acetylide chemistry to connect carbon fragments, or catalytic hydrogenation when reduction is the desired outcome.
These transformations are valuable when a synthesis requires access to alkenes, carbonyl compounds, or substituted alkynes from a common unsaturated starting point. The resulting flexibility supports reaction design and functional-group transformations across chemistry. The overview also identifies applications in pharmaceutical synthesis, materials development, and the preparation of molecular probes, where controlled structural changes are important.