Question

Using an oxidative cleavage reaction, explain how you would distinguish between the following two isomeric dienes:

Short answer

Answer

The reaction of given compounds with ${\mathrm{O}}_3$and Zn.

Step-by-step solution

O3 and Zn reactions

When an alkene is treated with ozone and subjected to reductive workup with zinc then the carbon-carbon double bond is cleaved to give ketones or aldehydes which depend on the structure of the alkene.

Oxidative cleavage reaction can be performed by ${\mathbf{O}}_{\mathbf{3}}$

 Step 2: Structure numbering

To distinguish these two structures we have given the number to the structure. Then we will study how we distinguish these two reactions with the help of reagents

Structure 1

Structure 2

Reaction with structure 1

Reagent ${\mathrm{O}}_3$ with Zn lead to the breaking of the double bond present in the structure 1 and lead to the formation of unsymmetrical aldehydes.

The reaction can be shown as:

${\mathrm{O}}_3$and Zn reaction

Reaction with structure 2

Reagent ${\mathrm{O}}_3$with Zn lead to the breaking of the double bond present in the structure 2 and lead to the formation of symmetrical aldehydes.

The reaction can be shown as:

${\mathrm{O}}_3$and Zn reaction

Reaction interpretation and reasoning

• To distinduish between the two structures we can perform oxidative cleavage by use of ${\mathrm{O}}_3$ and Zn.
• In this reaction, double bonds are broken between alkenes.
• As here double bonds are present at different locations so we will get different products.
• If on the first structure we perform ozonolysis then we will get Butane-1,4-dial and Ethane-1,4-dial.
• If on the second structure we perform ozonolysis then we will get2 Propane -1,3-dial.