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Prepared by Lawrence Kok

Video Tutorial on Nucleophilic Substitution, Free radical Substitution, Elimination, Addition Reactions In Organic Chemistry

IB Chemistry, Nucleophilic, Free radical Substitution, Elimination, Addition, Oxidation Reaction

Addition Reaction on Alkene

• C=C bond unsaturated, reactive due to weak pi bond

• C=C + HCl Chloroethane 

• C=C + Br2  Dibromoethane 

• C=C + H2O Ethanol (Alcohol)

• C=C + H2  Ethane (Alkane)

• C=C to C-C bond by Addition rxn

Oxidation Reaction on Alcohol

Alcohol - Hydrocarbon with

• hydroxyl functional group (OH) attach

• (1°, 2°, 3°) alcohol - number of alkyl gp attach to carbon bonded to OH

Oxidation of 1°, 2°, 3° alcohol• 1° alcohol (2 oxidisable H) to Aldehyde to Carboxylic acid

• 2° alcohol (1 oxidisable H) to Ketone

• 3° alcohol - no reaction

Oxidising agent used• Acidified Manganate (VII) ion (MnO4

−) from purple to pink

• Acidified Dichromate ion, (Cr2O72− ) from

orange to greenClick HERE more info

Substitution Reaction of Alkane (UV Free Radical)

Free Radical Substitution Initiation and Propagation step

• 3 stages, Initiation, Propagation and Termination

• Homolytic fission - Cl2 by UV form Cl. free radical

• Unpair electron, highly reactive

• CH4  + Cl2  CH3Cl  +  HCl

• Radical always react with a molecule to produce a radical and molecule again

• Cl. radical recycle/reacts again

Termination Step

• Radical with Radical forming a molecule (Termination)

Click HERE for more info

• CH4 in excess,- Chloromethane form

• CH4 + CI2   CH3Cl  +  HCl

• CH4 not in excess, - Dichloromethane form

• CH3CI + CI2  CH2CI2

• Tri and Tetrachloromethane will also form

Click HERE to view

Substitution Reaction on Halogenoalkane

Substitution on Bromoethane (C2H5-Br)

• Nucleophiles (electron donor) are OH-, CN-, NH3

 • SN2 mechanism

• C2H5-Br + OH-  C2H5-OH (ethanol)

• C2H5-Br + CN-  C2H5-CN (propanenitrile)

• C2H5-Br + NH3 --> C2H5-NH2 (ethylamine)

Nucleophilic Substitution -  

• Nucleophile, (donate non bonding electron) to partial positive charge carbon (nucleus) 

• Chloride (halogen) -  leaving group and substituted by nucleophile

• Nucleophile substitute the halogen 

Substitution of Bromoethane with warm aq dil NaOH by SN2

CH3CH2Br  + OH →  CH3CH2OH +  Br-

• Nucleophile OH-, substitute Br-

• One step mechanism

• Bond making/breaking simultaneous in transition state

Click HERE to view 

Elimination Reaction on Halogenoalkane

Substitution Reaction

• Using warm aq NaOH

• Nucleophile OH, donate e, forming dative bond with carbon

Elimination Reaction

• Using hot NaOH in ethanol 

• OH +C2H5OH C2H5O- (ethoxide) 

• Ethoxide acts as Base (donate e, forming dative bond with H)

• HBr is removed and C=C bond formed

Elimination Reactions

2 Bromopropane to Propene

• Symmetrical, give 1 product, Propene

• Ethoxide, as base removing H and Br, forming C=C bond

2 Bromobutane to 1 or 2 Butene 

• Unsymmetrical, give 2 products

• Ethoxide, as base has 2 ways to remove H and Br, forming 2 different products

• 1 Butene and 2 Butene formed

Click HERE  on elimination Bromopropane

Click HERE on elimination 2 Bromobutane

Mechanism for Substitution and Elimination

Substitution Mechanism

• Double arrow shows electron flow

• Nucleophile (OH, CN, NH3) donates e to carbon forming dative bond

• Bond forming and breaking in transition state

• C-OH bond form and C-Br bond break

Elimination Mechanism

• Ethoxide, base donate e to H

• Electron shift from Base to H to Br

• Br- ion leaves, forming C=C bond

Video, Elimination Mechanism, 2 Chlorobutane (For HL Chem)

Click HERE to view

Thanks to all pictures and video contributors used for the above post

Acknowledgements

Thanks to source of pictures and video used in this presentation

Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/

Prepared by Lawrence Kok

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