Chemistry Class 11 NCERT Solutions: Chapter 13 Hydrocarbons Part 5 (For CBSE, ICSE, IAS, NET, NRA 2022)

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


Q_5_Ans_1_Structure of Ethanal and Pentane - 3- One

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:

Q_5_Ans_2_Structure of Ozonide Cyclic Structure

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:

Q_5_Ans_3_Structure of 3 - Ethylpent - 2 -Ene

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

Q: 6. An alkene ‘A’ contains three , eight bonds and one 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 σ bonds. Hence, there are 8 hydrogen atoms in ‘A’ . Also, there are three bonds. Hence, there are four carbon atoms present in the structure of ‘A’ . Combining the inferences, the structure of ‘A’ can be represented as:

Q_6_Ans_1_Structure of but - 2 - Ene


‘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:

Q_6_Ans_1_Structure of Ethanal with Molecular Mass

The final product is ethanal with molecular mass

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