Question

Which alkene on reductive ozonolysis gives only propanone?

Answer 1

Hint: We know that as the name suggests, reductive ozonolysis; which is composed of ‘ozone’ and ‘lysis’ is a method to cleave a double or triple bond. The unsaturated bond breaks and links to ozone so as to form an intermediate, which leads to breaking up of the compound.

Complete answer: Ozonolysis is an organic reaction where the unsaturated bonds (double or triple bonds) of alkenes, alkynes, or azo compounds are cleaved by ozone. On ozonolysis alkenes and alkynes form organic compounds in which the carbon– carbon bond (double or triple) has been replaced by a carbonyl group. We can test the presence of double or triple bonds in the organic molecules by using ozonolysis.
Generally alkenes give aldehyde or ketone as the products on ozonolysis and alkynes give carboxylic acids as a product on ozonolysis. The ozonolysis is defined as a method of oxidatively cleaving alkenes or alkynes using ozone. This process allows for carbon-carbon double or triple bonds to be replaced by double bonds along with oxygen. This process cannot break a single bond because it is very stable.
Ozonides are formed by addition of the ozone molecule to double bond at alkene. It is practically obtained by passing a stream of ozone or ozonized oxygen on a solution of alkene which is in an inert solvent such as ether or carbon tetrachloride and adds ozone at double bond to give ozonides. Ozonides are unstable and highly reactive. Further it is either reduced with hydrogen in presence of catalysts such as palladium or on boiling in water with zinc dust to give carbonyl compounds as a product.
$$C{H}_3-C\left(C{H}_3\right)=C\left(C{H}_3\right)-C{H}_3\stackrel{O_3}{\to }2C{H}_3-C\left(C{H}_3\right)=O+H_{2}O$$
Therefore, $$2,3-dimethylbut-2-ene$$ gives only propane on ozonolysis.

Note:
Alkene: The chemical which contains double bonds in its structure is called alkene. Alkyne: The chemical which contains a triple bond in its structure is called alkyne. We can differentiate alkenes and alkynes very easily by using ozonolysis. On ozonolysis alkene gives aldehyde or ketone as the products. But alkynes give carboxylic acids on ozonolysis.