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A 3D model of ethyne (), the simplest alkyneIn organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. [1] The simplest acyclic alkynes with only one triple bond and no other functional groups form a homologous series with the general chemical formula C n H 2n−2.
Usually two equivalents of sodium amide yields the desired alkyne. Three equivalents are necessary in the preparation of a terminal alkynes because the terminal CH of the resulting alkyne protonates an equivalent amount of base. Hydrogen chloride and ethanol can also be eliminated in this way, [11] as in the preparation of 1-ethoxy-1-butyne. [12]
The mechanism of this transformation involves the addition of hydride to the carbon less able to stabilize the developing negative charge (viz., in the β position to an electron-withdrawing group). [10] Coordination of aluminium to the resulting trans vinyl carbanion leads to the observed trans configuration of the product. [11] (3)
For instance, oxidation of triphenylphosphine to triphenylphosphine oxide can lead to the formation of Pd 0 in situ when [Pd(PPh 3) 2 Cl 2] is used. Copper(I) salts, such as CuI, react with the terminal alkyne and produce a copper(I) acetylide, which acts as an activated species for the coupling reactions. Cu(I) is a co-catalyst in the reaction ...
The alkyne representation of benzyne is the most widely encountered. Arynes are usually described as having a strained triple bond. [6]Geometric constraints on the triple bond in benzyne result in diminished overlap of in-plane p-orbitals, and thus weaker triple bond. [7]
The alkyne zipper reaction requires a strong base, which can be generated from the reaction of potassium hydride and a diamine: [3] [1] Alkyne zipper reaction. The potassium 3-aminopropylamide deprotonates the less-substituted methylene adjacent to the alkyne group. [3] [1] Example mechanism for alkyne zipper reaction.
[3] [4] In the presence of unpolarized alkenes, alkynes or allenes, diimide is converted into dinitrogen with reduction (net addition of dihydrogen) of the unsaturated functionality. Diimide formation is the rate-limiting step of the process, and a concerted mechanism involving cis -diimide has been proposed. [ 5 ]
The nitrone-olefin (3+2) cycloaddition reaction is the combination of a nitrone with an alkene or alkyne to generate an isoxazoline or isoxazolidine via a (3+2) cycloaddition process. [1] This reaction is a 1,3-dipolar cycloaddition, in which the nitrone acts as the 1,3-dipole, and the alkene or alkyne as the dipolarophile.