Chapter 9 Solutions — Hydrocarbons

Exercises

1. 1.
   How do you account for the formation of ethane during chlorination of methane?
2. 2.
   Write IUPAC names of the following compounds:

   • (a) CH3CH=C(CH3)2
   • (b) CH2=CH-C≡C-CH3
   • (c) CH2=CH-CH=CH2 (buta-1,3-diene bond-line structure)
   • (d) benzene ring bearing a -CH2-CH2-CH=CH2 substituent
   • (e) benzene ring with -CH3 and -OH on adjacent (ortho) carbons
   • (f) CH3(CH2)4CH[CH2CH(CH3)2](CH2)3CH3
   • (g) CH3-CH=CH-CH2-CH=CH-CH(C2H5)-CH2-CH=CH2
3. 3.
   For the following compounds, write structural formulas and IUPAC names for all possible isomers having the number of double or triple bond as indicated:

   • (a) C4H8 (one double bond)
   • (b) C5H8 (one triple bond)
4. 4.
   Write IUPAC names of the products obtained by the ozonolysis of the following compounds:

   • (i) Pent-2-ene
   • (ii) 3,4-Dimethylhept-3-ene
   • (iii) 2-Ethylbut-1-ene
   • (iv) 1-Phenylbut-1-ene
5. 5.
   An alkene 'A' on ozonolysis gives a mixture of ethanal and pentan-3-one. Write structure and IUPAC name of 'A'.
6. 6.
   An alkene A contains three C-C sigma bonds, eight C-H bonds and one C=C pi bond. 'A' on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write IUPAC name of 'A'.
7. 7.
   Propanal and pentan-3-one are the ozonolysis products of an alkene. What is the structural formula of the alkene?
8. 8.
   Write chemical equations for combustion reaction of the following hydrocarbons:

   • (i) Butane
   • (ii) Pentene
   • (iii) Hexyne
   • (iv) Toluene
9. 9.
   Draw the cis and trans structures of hex-2-ene. Which isomer will have higher b.p. and why?
10. 10.
    Why is benzene extraordinarily stable though it contains three double bonds?
11. 11.
    What are the necessary conditions for any system to be aromatic?
12. 12.
    Explain why the following systems are not aromatic:

    • (i) Cyclobutadiene
    • (ii) A ring compound with an sp3 carbon (CH2 group in the ring)
    • (iii) A bicyclic non-planar system
13. 13.
    How will you convert benzene into

    • (i) p-nitrobromobenzene
    • (ii) m-nitrochlorobenzene
    • (iii) p-nitrotoluene
    • (iv) acetophenone?
14. 14.
    In the alkane H3C-CH2-C(CH3)2-CH2-CH(CH3)2, identify primary, secondary, tertiary and quaternary carbon atoms and give the number of H atoms bonded to each one.
15. 15.
    What effect does branching of an alkane chain have on its boiling point?
16. 16.
    Addition of HBr to propene yields 2-bromopropane, while in the presence of benzoyl peroxide, the same reaction yields 1-bromopropane. Explain and give mechanism.
17. 17.
    Write down the products of ozonolysis of 1,2-dimethylbenzene (o-xylene). How does the result support Kekulé structure for benzene?
18. 18.
    Arrange benzene, n-hexane and ethyne in decreasing order of acidic behaviour. Also give reason for this behaviour.
19. 19.
    Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?
20. 20.
    How would you convert the following compounds into benzene?

    • (i) Ethyne
    • (ii) Ethene
    • (iii) Hexane
21. 21.
    Write structures of all the alkenes which on hydrogenation give 2-methylbutane.
22. 22.
    Arrange the following set of compounds in order of their decreasing relative reactivity with an electrophile E+:

    • (a) Chlorobenzene, 2,4-dinitrochlorobenzene, p-nitrochlorobenzene
    • (b) Toluene, p-nitrotoluene, p-dinitrobenzene
23. 23.
    Out of benzene, m-dinitrobenzene and toluene which will undergo nitration most easily and why?
24. 24.
    Suggest the name of a Lewis acid other than anhydrous aluminium chloride which can be used during ethylation of benzene.
25. 25.
    Why is Wurtz reaction not preferred for the preparation of alkanes containing odd number of carbon atoms? Illustrate your answer by taking one example.