use of polythene and polypropylene is a matter of great concern for all of us. . Alkynes Like alkenes, alkynes are also unsaturated hydrocarbons. They contain at least one triple bond between two carbon atoms.
The number of hydrogen atoms is still less in alkynes as compared to alkenes or alkanes. Their general formula is C n H 2n– . The first stable member of alkyne series is ethyne which is popularly known as acetylene. Acetylene is used for arc welding purposes in the form of oxyacetylene flame obtained by mixing acetylene with oxygen gas.
Alkynes are starting materials for a large number of organic compounds. Hence, it is interesting to study this class of organic compounds. . .
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 a few members of alkyne series are given in Table .
. You have already learnt that ethyne and propyne have got only one structure but there are two possible structures for butyne – (i) but- -yne and (ii) but- -yne. Since these two compounds differ in their structures due to the position of the triple bond, they are known as position isomers . In how many ways, you can construct the structure for the next homologue i.e., the next alkyne with molecular formula C H ?
Let us try to arrange five carbon atoms with a continuous chain and with a side chain. Following are the possible structures : Structure IUPAC name I. HC ≡ C– CH – CH – CH Pent– -yne II. H C–C ≡ C– CH – CH Pent– -yne III.
H C–CH–C ≡ CH -Methyl but– -yne Structures I and II are position isomers and structures I and III or II and III are chain isomers. Problem . Write