alkynider

Alkynider, or alkynes in English, are a class of hydrocarbons characterized by the presence of at least one carbon‑carbon triple bond. The simplest alkyne is acetylene (ethyne), C2H2, which contains a triple bond between the two carbon atoms. In general, alkynes have the molecular formula CnH2n−2, indicating that each triple bond eliminates two hydrogen atoms compared to the corresponding alkane. The triple bond consists of one sigma and two pi bonds, giving alkynes a linear geometry around the bonded carbons with bond angles of approximately 180°. This geometry also accounts for the reactivity of the pi bonds in alkynes toward electrophilic addition reactions.

Alkynes can be synthesized by several routes, including dehydrohalogenation of vicinal dihalides, elimination reactions of haloalkanes, and the thermal or catalytic cracking of larger hydrocarbons. Acetylene is commonly produced by the catalytic partial oxidation of methane or by the reaction of calcium carbide with water. Functionalization of alkynes is a major area of organic synthesis; typical transformations include hydrohalogenation, hydration, halogenation, and the formation of ketones via oxidation with acidified silver oxide (Prins–Yost oxidation). Metal-catalyzed cross-coupling reactions, such as Sonogashira and Glaser couplings, allow the construction of carbon‑carbon bonds involving alkynyl groups.

Because of their high bond order and linear shape, alkynes exhibit distinct physical properties: they are usually gases or volatile liquids, with lower boiling points than alkanes of comparable molecular weight. Their spectroscopic features, notably a sharp absorption near 2200 cm−1 in the infrared for the C≡C stretching vibration and a characteristic chemical shift around 2.5 ppm in proton NMR for terminal alkynes, aid in their identification. Alkynes are used industrially as building blocks for polymers, pharmaceuticals, and as precursors for more elaborate organic molecules.