Properties of Alkynes:
Alkynes, often called acetylenes, are hydrocarbons with carbon-carbon triple bonds. Alkynes have two Sp hybridized orbitals and 2 p orbitals, and have bond angles of 180 degrees.
 Kekule Structure |
 Lewis Dot Structure |
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Unlike carbon-carbon single bonds, triple and double bonds do not have free bond rotation, and have shorter bond lengths. This is due to the rigidity of the triple bond.
Examining the bond dissociation energies, we find that the dissociation energy of a single bond is much higher than that of a triple bond, about 20kcal/mol more. This means that double bonds are significantly more reactive than single bonds, classifying it as a functional group.
Nomenclature of Alkynes:
Naming of alkynes is very similar to the naming of alkenes, using the root name of the longest carbon chain. The ending, however, is changed from -ene to -yne, and a number is given to show the location of the triple bond for molecules of more than three base carbons. |
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ethyne (There
is no need for a number. A one is implied. )
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Propyne (one is implied) | 2-Butyne |
Common Nomenclature:
Often, alkynes are named
with a base name of acetylene, the simplest alkyne. Then
substituents are added.
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| Acetylene | Methyl acetylene | Dimethyl Acetylene |
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