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Chapter Analysis
Advanced33 pages • EnglishQuick Summary
The chapter on Hydrocarbons covers various types of hydrocarbons, their properties, and reactions. It explains the classification of hydrocarbons into alkanes, alkenes, and alkynes, and delves into the mechanism of electrophilic substitution in aromatic hydrocarbons. The chapter also includes discussions on isomerism and the applications of hydrocarbons as fuels and in other industries. Additionally, the environmental impact, including carcinogenicity of certain hydrocarbons, is discussed.
Key Topics
- •Classification of hydrocarbons
- •Reactions of hydrocarbons
- •Aromatic hydrocarbons and aromaticity
- •Isomerism in hydrocarbons
- •Electrophilic substitution mechanisms
- •Carcinogenicity of hydrocarbons
- •Combustion of hydrocarbons
- •Nomenclature and isomerism in alkanes
Learning Objectives
- ✓Name hydrocarbons according to the IUPAC system of nomenclature
- ✓Distinguish between alkanes, alkenes, alkynes, and aromatic hydrocarbons
- ✓Understand the role of hydrocarbons as energy sources
- ✓Comprehend the structure and aromaticity of benzene
- ✓Predict the formation of addition products of unsymmetrical alkenes
- ✓Recognize the carcinogenicity and toxicity of polynuclear hydrocarbons
Questions in Chapter
How do you account for the formation of ethane during chlorination of methane?
Page 326
Write IUPAC names of the following compounds: (a) CH3CH=C(CH3)2 (b) CH2=CH-C≡C-CH3
Page 326
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)
Page 326
Write IUPAC names of the products obtained by the ozonolysis of the following compounds.
Page 326
An alkene ‘A’ on ozonolysis gives a mixture of ethanal and pentan-3-one. Write structure and IUPAC name of ‘A’.
Page 327
An alkene ‘A’ contains three C – C, eight C – H σ bonds and one C – C π bond. ‘A’ on ozonolysis gives two moles of an aldehyde of molar mass 44 u. Write IUPAC name of ‘A’.
Page 327
Propanal and pentan-3-one are the ozonolysis products of an alkene? What is the structural formula of the alkene?
Page 327
Write chemical equations for combustion reaction of the following hydrocarbons: (i) Butane (ii) Pentene (iii) Hexyne (iv) Toluene
Page 327
Draw the cis and trans structures of hex-2-ene. Which isomer will have higher b.p. and why?
Page 327
Why is benzene extraordinarily stable though it contains three double bonds?
Page 327
What are the necessary conditions for any system to be aromatic?
Page 327
Explain why the following systems are not aromatic?
Page 328
How will you convert benzene into (i) p-nitrobromobenzene (ii) m-nitrochlorobenzene (iii) p-nitrotoluene (iv) acetophenone?
Page 328
In the alkane H3C – CH2 – C(CH3)2 – CH2 – CH(CH3)2, identify 1°, 2°, 3° carbon atoms and give the number of H atoms bonded to each one of these.
Page 328
What effect does branching of an alkane chain have on its boiling point?
Page 328
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.
Page 328
Write down the products of ozonolysis of 1,2-dimethylbenzene (o-xylene). How does the result support Kekulé structure for benzene?
Page 328
Arrange benzene, n-hexane and ethyne in decreasing order of acidic behaviour. Also give reason for this behaviour.
Page 328
Why does benzene undergo electrophilic substitution reactions easily and nucleophilic substitutions with difficulty?
Page 329
Additional Practice Questions
What are the physical properties that distinguish alkanes from alkenes?
mediumAnswer: Alkanes are generally less dense and more viscous than alkenes. They have single bonds allowing free rotation which results in less interaction between molecules compared to alkenes with double bonds. This makes alkenes more likely to be liquids at room temperature than alkanes of similar size.
Describe the combustion process of hydrocarbons and the factors affecting it.
mediumAnswer: Combustion of hydrocarbons involves burning in the presence of oxygen to produce carbon dioxide, water, and energy. Factors affecting combustion include the availability of oxygen, the temperature, and the surface area of the hydrocarbon.
Explain the difference between electrophilic and nucleophilic reactions.
mediumAnswer: In electrophilic reactions, the reactant seeks electrons and is attracted to regions of high electron density. In nucleophilic reactions, the reactant donates electrons and attacks regions of low electron density, typically forming bonds by donating an electron pair.
Why do aromatic hydrocarbons generally undergo substitution rather than addition reactions?
hardAnswer: Aromatic hydrocarbons, like benzene, prefer substitution reactions to maintain their aromatic stability. Addition reactions would disrupt the delocalized π-electron cloud and aromaticity.
How does the structure of benzene contribute to its chemical properties?
hardAnswer: Benzene's structure, with delocalized π-electrons across a six-carbon ring, gives it unique stability and aromatic character, influencing its tendency to undergo electrophilic substitution.