Nomenclature and Isomerism

In common system, alkynes are named as derivatives of acetylene. In IUPAC system, they are named as derivatives of the corresponding alkanes replacing ‘ane’ by the suffix ‘yne’. The position of the triple bond is indicated by the first triply bonded carbon.

Common and IUPAC Names of Alkynes (C_nH_2n–2)

Ethyne and propyne have got only one structure but there are two possible structures for butyne –

· but-1-yne

· but-2-yne

Since these two compounds differ in their structures due to the position of the triple bond, they are known as position isomers. The ways to construct the structure for the next homologue i.e., the next alkyne with molecular formula C₅H₈. Let us try to arrange five carbon atoms with a continuous chain and with a side chain. Following are the possible structures :

Structures I and II are position isomers and structures I and III or II and III are chain isomers.