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Nomenclature and Isomerism

The IUPAC name of an alkyne is derived from the name of the corresponding alkane by replacing suffix-ane by yne.

 

In common system, the name of the simplest alkyne is acetylene. The names of the higher alkynes are given as substituted acetylenes.

Some members of homologous series of alkynes are given below:

Ethyne and propyne have only one structural formula and hence they do not exhibit isomerism. Butyne can have two structures as shown below:

Compounds having molecular formula CnH2n are alkenes. Thus, C4H8 and C5H10 are alkenes. Compounds having molecular formula cnH2n- 2 are alkynes. Thus, C7H12 and C2~ are alkynes.

But-1-yne and but-2-yne are position isomers as they differ in the position of the triple bond. The higher alkynes can exhibit chain isomerism in addition to position isomerism. For example, for pentyne , C5H8 the following isomeric alkynes are possible.

The compounds I and II are position isomers. The compounds I and III or II and III are chain isomers.