Chemistry Class 11 NCERT Solutions: Chapter 13 Hydrocarbons Part 6

Q: 7. Propanal and pentan-3-one are the ozonolysis products of an alkene? What is the structural formula of the alkene?

Answer:

As per the given information, propanal and pentan-3-one are the ozonolysis products of an alkene. Let the given alkene be ‘A’. Writing the reverse of the ozonolysis reaction, we get:

The products are obtained on the cleavage of ozonide ‘X’. Hence, ‘X’ contains both products in the cyclic form. The possible structure of ozonide can be represented as:

Now, ‘X’ is an addition product of alkene ‘A’ with ozone. Therefore, the possible structure of alkene ‘A’ is:

Q: 8. Write Chemical equations for combustion reaction of the following hydrocarbons

(I) Butane

(II) Pentene

(III) Hexyne

(IV) Toluene

Answer:

Combustion can be defined as a reaction of a compound with oxygen.

(I) Equation

(II) Equation

(III) Equation

(IV)

Q: 9. Draw the Equation and Equation structures of hex-2-ene. Which isomer will have higher b.p. and why?

Answer:

Hex-2-ene is represented as:

Equation

Geometrical isomers of hex-2-ene are:

The dipole moment of cis-compound is a sum of the dipole moments of Equation and Equation bonds acting in the same direction. The dipole moment of trans-compound is the resultant of the dipole moments of Equation and Equation bonds acting in opposite directions. Hence, cis-isomer is more polar than trans-isomer. The higher the polarity, the greater is the intermolecular dipole-dipole interaction and the higher will be the boiling point. Hence, cis-isomer will have a higher boiling point than trans-isomer.

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