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In organic chemistry, an alkyne is an unsaturated carbon containing at least one carbon-carbon triple bond is present. The simplest acyclic alkynes have only one triple bond and no other functional group attached form a homologous series with the general chemical formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known widely as ethyne using IUPAC nomenclature. Like other hydrocarbons, alkynes are generally hydrophobic in nature.
Structure And Bonding of Alkyne
In acetylene, the H–C≡C-H bond angle is 180°. By this bond angle, alkynes are rod-like shapes. Hence, the cyclic alkynes are rare. The C≡C bond distance of 121 picometers is much shorter than the C=C distance in alkenes which is 134 picometers, or the C–C bond in alkanes which is 153 picometers.
The triple bond is very strong having a bond strength of 839 kJ/mol. The sigma bond contributes 369 kJ/mol, the first pi bond contributes 268 kJ/mol, and the second pi-bond has 202 kJ/mol of bond strength. Bonding is usually discussed in the context of the molecular orbital theory, which recognizes the triple bond as arising from the overlap of the s and p orbitals. In the language of valence bond theory, the carbon atoms in an alkyne bond are sp hybridized: they each have two unhybridized p orbital and two sp hybrid orbitals in it. The Overlap of an sp orbital from each atom forms one sp–sp sigma-bong. Each p orbital on one atom overlaps on the other atom, forming two pi-bonds, giving a total of three bonds. The remaining sp orbital on each atom can form a sigma bond to the other atom, for example, hydrogen atoms in the parent acetylene. The two sp orbitals project on opposite sides of a carbon atom.
Terminal And Internal Alkynes
The Internal alkynes feature carbon substituents on each acetylenic carbon. The Symmetrical examples include 3-hexyne and diphenylacetylene.
The Terminal alkynes have the formula RC2H. For example, take methylacetylene (propyne using IUPAC nomenclature). The Terminal alkynes, like acetylene itself, are mildly acidic, with pKa values of around 25. They are far more acidic than alkenes and alkanes, which have pKa values of 40 and 50, respectively. The acidic hydrogen on terminal alkynes can be replaced by many groups resulting in halo-, silyl-, and alkoxy alkanes. The carbanions generated by deprotonation of the terminal alkynes are called acetylides.
Diphenylacetylene
It is a chemical compound having a formula of C6H5C≡CC6H5. The molecule consists of two phenyl groups attached to the C2 unit. A colorless solid, it is used as a building block in organic synthesis and as a ligand in organometallic chemistry.
In preparation of Diphenylacetylene, benzil is condensed with hydrazine to give the bis(hydrazone), which is then oxidized with mercury(II) oxide. Alternatively, stilbene is brominated, and the resulting dibromo diphenylethane is subjected to dehydrohalogenation, Yet the other method starts involves the coupling of iodobenzene and the copper salt of phenylacetylene in Castro-Stephens coupling.
It is a plane molecule. The distance between C≡C is 119.8 picometers
3-Hexyne
The 3-Hexyne is an organic compound with the formula C2H5CCC2H5. This colorless liquid and it is one of three isomeric hexynes. The 3-Hexyne forms with 5-decyne, 4-octyne, and 2-butyne is a series of symmetric alkynes. It is like a reagent in organometallic chemistry.
- formula: C6H10
- molecular weight: 82.1436
- IUPAC Standard InChI: InChI=1S/C6H10/c1-3-5-6-4-2/h3-4H2,1-2H3 Copy
- IUPAC Standard InChIKey: DQQNMIPXXNPGCV-UHFFFAOYSA-N Copy
- CAS Registry Number: 928-49-4
- Chemical structure:
- Other names: Diethylacetylene; C2H5C≡CC2H5; Hex-3-yne
Description
The 3-Hexyne was used in the synthesis of fused hetero-hydropyridyl ligands bonded to the {Ru(p-cymene)} organometallic moiety by reacting with ruthenacycles. It was also used in the preparation of [4+2] cycloaddition products by combining it with borole.
Conclusion
The Internal alkynes feature carbon substituents on each acetylenic carbon. The Symmetrical examples include 3-hexyne and diphenylacetylene. The Terminal alkynes have the formula RC2H. For example methylacetylene (propyne using IUPAC nomenclature). In other words Terminal alkynes (e.g., but-1-yne) have acidic H atoms and give an insoluble white precipitate of silver alkynide with an alcoholic solution of AgNO3 and NH3, whereas internal alkynes (e.g., but-2-yne) have no acidic or H atom and do not react to give a precipitate after the process. Diphenylacetylene is the compound having the formula C6H5C≡CC6H5. The molecule consists of two phenyl groups attached to the C2 unit. A colorless solid, it is used as a building block in organic synthesis and as a ligand in organometallic chemistry.
The 3-Hexyne is an organic compound with the formula C2H5CCC2H5. This colorless liquid is one of three isomeric hexynes. The 3-Hexyne forms with 5-decyne, 4-octyne, and 2-butyne is a series of symmetric alkynes. It is like a reagent in organometallic chemistry.
