Chemistry Class 11 NCERT Solutions: Chapter 13 Hydrocarbons Part 5

Q: 5. An alkene ‘A’ on ozonolysis gives a mixture of ethanal and pentane -3- one. Write structure and IUPAC name of ‘A’.


During ozonolysis, an ozonide having a cyclic structure is formed as an intermediate, which undergoes cleavage to give the final products. Ethanal and pentan-3-one are obtained from the intermediate ozonide. Hence, the expected structure of the ozonide is:

This ozonide is formed as an addition of ozone to ‘A’. The desired structure of ‘A’ can be obtained by the removal of ozone from the ozonide. Hence, the structural formula of ‘A’ is:

The IUPAC name of ‘A’ is 3 – Ethylpent -2 – ene

Q: 6. An alkene ‘A’ contains three Equation , eight Equation bonds and one Equation bond. ‘A’ on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write IUPAC name of ‘A’.


As per the given information, ‘A’ on ozonolysis gives two moles of an aldehyde of molar mass 44 u. The formation of two moles of an aldehyde indicates the presence of identical structural units on both sides of the double bond containing carbon atoms. Hence, the structure of ‘A’ can be represented as:


There are eight Equation σ bonds. Hence, there are 8 hydrogen atoms in ‘A’. Also, there are three Equation bonds. Hence, there are four carbon atoms present in the structure of ‘A’. Combining the inferences, the structure of ‘A’ can be represented as:


‘A’ has 3 C–C bonds, 8 C–H σ bonds, and one C–C π bond.

Hence, the IUPAC name of ‘A’ is But-2-ene.

Ozonolysis of ‘A’ takes place as:

The final product is ethanal with molecular mass



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