VJC 2024 Alkanes Lecture Notes

VICTORIA JUNIOR COLLEGE CHEMISTRY DEPARTMENT Mr. Rafiqi [muhammad.rafiqi.leman@vjc.edu.sg] H2 ORGANIC CHEMISTRY: ALKANES Lecture Outline 1 Introduction 2 Cycloalkanes 3 Physical Properties 4 Preparation 5 Reactions 5.1 Combustion 5.11 Limited supply of oxygen 5.12 Unlimited supply / excess of oxygen 5.2 Formation of Halogenoalkanes 5.21 Free radical substitution mechanism 5.22 Reactivity of halogens 5.23 Rate of substitution at primary, secondary and tertiary carbon atoms 6 Petroleum and its Environmental Consequences 6.1 Environmental Pollutants 6.2 Use of Catalytic Converter 6.3 Enhanced Greenhouse Effect Assessment Objectives Candidates should be able to: (a) explain the general unreactivity of alkanes, including towards polar reagents (b) describe the chemistry of alkanes as exemplified by the following reactions of ethane: (i) combustion (ii) free–radical substitution by chlorine and by bromine (c) describe the mechanism of free –radical substitution with particular reference to the initiation, propagation and termination reactions (d) recognise the environmental consequences of: (i) carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising from the internal combustion engine and of their catalytic removal (ii) gases that contribute to the enhanced greenhouse effect (e) recognise that petroleum, a chemical feedstock, is a finite resource and the importance of recycling References 1 Chemistry in Action by Michael Freemantle 2 ‘A’ Level Chemistry by E.N. Ramsden 3 Chemistry – Longman ‘A’ Level Guides by J.G.R. Briggs 4 Organic Chemistry by H.L. Heys 5 Organic Chemistry by B.J. Stokes Lecture 1 2 Pages 1–8 8–15 Complete by T3W7 T3W8 Tutorial Qns 1–2 3–8

2 Hydrocarbons (Compounds containing only carbon and hydrogen atoms) Aliphatic hydrocarbon Alicyclic hydrocarbon Aromatic hydrocarbon or Arenes (Benzene and its alkyl derivatives) 1. Alkanes 2. Alkenes 1. Cycloalkanes E.g. cyclohexane 2. Cycloalkenes E.g. cyclohexene 1 and 2 contain rings of carbon atoms. 1. Benzene 2. Benzene derivatives E.g. methylbenzene 3. Naphthalene and others ALKANES 1 Introduction • Homologous series of saturated aliphatic hydrocarbon of general formula CnH2n+2. • Names of alkanes end with ‘ane’. n molecular formula name structural formula 1 CH4 methane CH4 2 C2H6 ethane CH3CH3 3 C3H8 propane CH3CH2CH3 4 C4H10 butane CH3(CH2)2CH3 5 C5H12 pentane CH3(CH2)3CH3 6 C6H14 hexane CH3(CH2)4CH3 7 C7H16 heptane CH3(CH2)5CH3 8 C8H18 octane CH3(CH2)6CH3 • Constitutional isomerism exists in alkanes containing more than three carbon atoms due to branching of chains. E.g. C4H10 (butane) has 2 constitutional isomers. straight chain branched chain C H H CH H H C H H C H H H

3 E.g. C5H12 (pentane) has 3 constitutional isomers. straight chain branch