2-methyl-2-pentene from Propyne | Propene Isomers

Synthesis 2-methyl-2-pentene from propyne. You can use any organic reagents for this organic conversion. But note that you have to start the conversion with propyne.

In the IUPAC nomenclature, 2-methyl-2-pentene is now expressed as 2-methylpent-2-ene.

In this tutorial, we will learn how to prepare 2-methyl-2-pentene and will discuss isomerism of pentene and pentyne.


2-methyl-2-pentene is an alkene compound. A -CH3 group is attached as a substitution group to the major group. There are five carbon atoms contain in the major branch.


Preparing 2-methyl-2-pentene

IUPAC name of 2-methyl-2-pentene demonstrates an alkene compound. We have synthesis 2-methyl-2-pentene from propyne. Propyne and 2-methyl-2-pentene contain 3 and 6 carbon atoms respectively. Number of carbon atoms of propyne is doubled when 2-methyl-2-pentene is prepared. But propyne cannot straightly doubled to give 2-methyl-2-pentene.

propyne to 2-methyl-2-pentene

Preparing 2-methyl-2-pentene from propyne

Each stepes of preparing 2-methyl-2-pentene from propyne is explained below.

Propyne hydrolysis

Alkyne hydrolysis is done by HgSO4 and dilute H2SO4 and give aldehyde or ketone as products. Propyne hydrolysis gives propanone as the product. Here, HgSO4 and dilute H2SO4 behave as catalysts.

Propanone aldol condensation with dilute NaOH

Aldehyde or ketone react with dilute NaOH to give compounds with longer carbon chains. (Aqueous KOH also can be used instead of NaOH).

Heating the solution

Solution is heated with I2 or alone to dehydrate the -OH bond. A double bond forms. The carbonyl group exists without any change.

Clemmensen reduction

Aldehyde or ketone can be reduced to hydrocarbons using clemmensen reduction. This reaction is called clemmensen reduction. Zn(Hg) and concentrated HCl is used as the reagent. So given aldol product is reduced by Clemmensen reduction. Otherwise we can simply this by reducing -CHO to -CH2.

propyne to 2-methyl-2-pentene conversion

Physical properties of 2-methyl-2-pentene from propyne

  • 2-methyl-2-pentene is a liquid and from propyne is a gas at room temperature.
  • 2-methyl-2-pentene is an alkene and propyne is an alkyne.

Chemical properties of 2-methyl-2-pentene from propyne

  • Propyne reacts with sodium. But 2-methyl-2-pentene does not react.
  • Both compounds react with liquid Br2 / CCl4.
  • Alkyne hydration is more difficult than alkene hydration.

Isomers of 2-methyl-2-pentene

There are no optical isomerism and geometric isomerism of 2-methyl-2-pentene. So no stereo isomerism in the 2-methyl-2-pentene.

Pentene isomers

We can change the double bond and location of carbon groups to draw different isomers for pentene, the alkene which has five carbon atoms.

pentene isomers

Organic conversions exercises