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Alkanes and Alkenes. PropertyAlkaneAlkene Reactions involve heterolytic fisson Free Radical Substitution reaction Formed during cracking reactions Exist.

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Presentation on theme: "Alkanes and Alkenes. PropertyAlkaneAlkene Reactions involve heterolytic fisson Free Radical Substitution reaction Formed during cracking reactions Exist."— Presentation transcript:

1 Alkanes and Alkenes

2 PropertyAlkaneAlkene Reactions involve heterolytic fisson Free Radical Substitution reaction Formed during cracking reactions Exist as Stereoisomers Electrophilic addition reactions take place Exist as Structural isomers Exist as Cis/trans or E/Z isomers Has 1 pi Molecular orbital Has all single bonds Decolourises bromine in absence of UV Has sigma molecular orbitals Reactions involve homolytic fisson Substitution reactions occur Addition reactions occur Burn to give carbon dioxide and water in a good supply of air Undergo polymerisation reactions

3 Processing Alkanes CRACKING, REFORMING, ISOMERISATION How is it carried out? C – Al 2 O 3 and heat R – Pt/Rh and heat I – Pt separated by zeolyte catalyst and heat What are the products? C – Smaller Alkanes AND alkenes R – Cyclic alkanes and hydrogen I – Branched alkane isomers of original Why is it carried out? C – Smaller Alkanes used as fuels, alkenes used to make polymers R – Lowers bp of alkane so more vapour at same temp so better ignition (Weaker VDW as smaller molecule) I – Lowers bp of alkane so more vapour at same temp so better ignition (Weaker VDW as molecules pack together less well)

4 CH 4 + Cl 2 CH 3 Cl + HCl Overall reaction equation Conditions ultra violet light excess methane i.e. homolytic breaking of covalent bonds to reduce further substitution Free radical substitution chlorination of methane

5 CH 4 + ClCH 3 + HCl Cl 2 Cl + Cl CH 3 + Cl 2 CH 3 Cl + Cl CH 3 ClCH 3 + Cl initiation step two propagation steps termination step ultra-violet CH 3 CH 3 + CH 3 minor termination step Free radical substitution mechanism

6 CH 3 Cl + Cl 2 CH 2 Cl 2 + HCl Overall reaction equations Conditionsultra-violet light CH 2 Cl 2 + Cl 2 CHCl 3 + HCl CHCl 3 + Cl 2 CCl 4 + HCl excess chlorine Further free radical substitutions

7 Electrophilic addition CH 2 =CH 2 + Br 2 CH 2 BrCH 2 Br bromine with ethene 1,2-dibromoethane Overall reaction equation mechanism

8 Br Electrophilic addition mechanism H H H H C C δ+ δ- H H H H C C Br + - carbocation H H H H C C Br 1,2-dibromoethane bromine with ethene reaction equation

9 Electrophilic addition 2 CH 3 CH=CH 2 + HBr CH 3 CH 2 CH 2 Br Hydrogen bromide with propene 1-bromopropane or Overall reaction equation mechanism CH 3 CHBrCH 3 2-bromopropane Conditions DRY HBr in Ethanol

10 Electrophilic addition mechanism H H CH 3 H C C Br H δ+ δ- H H CH 3 H C C H + Br - H H CH 3 H C C BrH 1-bromopropane Hydrogen bromide with Propene reaction equation Br H δ+ δ-

11 Electrophilic addition mechanism H H CH 3 H C C Br H δ+ δ- H CH 3 H H C C H + Br - H CH 3 H H C C BrH 2-bromopropane Hydrogen bromide with Propene reaction equation Br H δ+ δ-


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