Introduction to the Alkynes

James Richard Fromm


Alkynes are hydrocarbons which contain a triple carbon-carbon bond. As with alkenes, the simplest member of the series is the two-carbon molecule. The triple bond is indicated by changing the ending of the name to -yne, in the same manner as the double bonds in alkenes are indicated by the ending -ene.  Alkynes, like alkenes are unsaturated hydrocarbons with the general formula CnH2n-2.   They are very unstable and quite reactive. For example, ethyne the simplest alkyne,

ethyne.jpg (2350 bytes)

 Structure of Ethyne, Acetylene

which is more commonly known by its common name acetylene, is a gas often used as a fuel for cutting and welding torches because it burns with a very hot flame.

The alkynes follow much the same pattern of reactivity and nomenclature as do the alkenes. However, the alkynes which have the triple bond at the end of the molecule often have the terminal hydrogen relatively acidic, while no other hydrogen on the alkyne or on the corresponding alkene is even slightly acidic. This acidity arises because the bonding electrons of the terminal hydrogen tend to associate themselves with the electrons in the triple bond, lending a considerable ionic character to the bond to hydrogen.

Alkynes
Ethyne C2H2
Propyne C3H4
Butyne C4H6
Pentyne C5H8
Propyne2.gif (418 bytes)
Propyne

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Copyright 1997 James R. Fromm