Question

The products obtained on ozonolysis of 2-ehtylbut-1-ene are:
[A] Propanone and ethanal
[B] Ethanal and 3-pentanone
[C] Butanal and ethanal
[D] Methanal and 2-pentanone
[E] Methanol and 3-pentanone

Answer 1

Hint: Ozonolysis is the process of cleaving the double bond by the formation of a five membered ring. Here the ring will be formed including the carbon atoms included in the double bonding. Upon ozonolysis of 2-ethylbut-1-ene we receive two products one is a ketone and the other is an aldehyde.

Complete Step by Step Solution: Before answering the question, let us understand what ozonolysis reaction is.
To break a double bond we need to carry the process by two successive oxidations. First oxidation is of the –pi bond and the second is of the –sigma bond. This is called double oxidation.
 We can carry out this oxidation in a single step by ozone.
We know that ozone is a symmetrical bent molecule with a central positively charged oxygen atom and the other two oxygen atoms i.e. the terminal oxygen atoms share a negative charge. Ozone is unstable and we generate it immediately before use from oxygen using a device called ozonizer. Then it is bubbled into the reaction mixture.
We add $Os{{O}_{4}}$ to alkenes and it is added by a cyclic mechanism making a five membered ring with the three oxygen atoms. This structure is extremely unstable and collapses by breaking a weak O – O bond and a C – C sigma bond but gains two strong –C=O bonds in this process.
We get an aldehyde and an unstable carbonyl oxide as products. When we add a mild reducing agent to this, the carbonyl oxide is also converted to aldehyde thus giving us two aldehydes.
This process of bond cleaving in alkenes is known as ozonolysis. Now let us discuss the ozonolysis of 2-ethylbut-1-ene.
Firstly, we know that the structure of 2-ethylbut-1-ene is-

Now let us see the process of its ozonolysis-

We can see from the above reaction that the products formed are 3-pentanone and methanal.

Therefore, the correct answer is option [E] Methanol and 3-pentanone.

Note: We can use ozonolysis to produce not only aldehydes but other functional groups too like carboxylic acids by completing the reaction with oxidizing agents and alcohols by completing the reaction with a strong reducing agent.
Ozonolysis of cyclohexenes is an important reaction as it gives 1,6-dicarbonyl compounds that are very difficult to make by any other reaction.