Question

How many different acyclic isomers of ${{\text{C}}_{\text{6}}}{{\text{H}}_{{\text{12}}}}$ on hydrogenation with ${{\text{H}}_{\text{2}}}{\text{/Ni}}$ gives the same 3-methyl pentane?

Answer 1

Hint:Compounds that have identical chemical formula but different structures are known as isomers of each other. Alkanes are obtained by the hydrogenation of alkenes.

Complete step by step answer:
The product obtained is 3-methyl pentane. In 3-methyl pentane, the parent compound is pentane which suggests that 3-methyl pentane is an alkane.
The structure of 3-methyl pentane is,

3-methyl pentane is obtained by hydrogenation of alkenes with ${{\text{H}}_{\text{2}}}$ in presence of nickel as a catalyst. All the alkenes are acyclic isomers of ${{\text{C}}_{\text{6}}}{{\text{H}}_{{\text{12}}}}$.
The alkenes which are acyclic isomers of ${{\text{C}}_{\text{6}}}{{\text{H}}_{{\text{12}}}}$ are as follows:
1.(S)-3-methylpent-1-ene
2.(R)-3-methylpent-1-ene
3.3-methylpentane
4.(Z)-3-methylpent-2-ene
5.(E)-3-methylpent-2-ene
The structures of the acyclic isomers are as follows:

Note: The hydrogenation of alkenes with ${{\text{H}}_{\text{2}}}$ in presence of nickel as a catalyst gives alkanes. The ${{\text{H}}_{\text{2}}}$ gets added across the carbon-carbon double bond resulting in formation of an alkane. Thus, hydrogenation of an alkene is an addition reaction.
The hydrogenation of alkynes with ${{\text{H}}_{\text{2}}}$ in presence of nickel as a catalyst gives alkenes. The ${{\text{H}}_{\text{2}}}$ gets added across the carbon-carbon triple bond resulting in formation of an alkene. Thus, hydrogenation of an alkyne is an addition reaction.