OCR organic reaction mechanisms Click a box below to go to the mechanism Click here for advice AS Free Radical Substitution Electrophilic Addition Nucleophilic Substitution A2 Electrophilic Substitution Nucleophilic Addition

Free radical substitution chlorination of methane i.e. homolytic breaking of covalent bonds Overall reaction equation CH4 + Cl2 CH3Cl + HCl Conditions ultra violet light excess methane to reduce further substitution

Free radical substitution mechanism ultra-violet Cl2 Cl + Cl initiation step two propagation steps CH4 + Cl CH3 + HCl CH3 + Cl2 CH3Cl + Cl termination step CH3 + Cl CH3Cl CH3 + CH3 CH3CH3 minor termination step

Further free radical substitutions Overall reaction equations CH3Cl + Cl2 CH2Cl2 + HCl CH2Cl2 + Cl2 CHCl3 + HCl CHCl3 + Cl2 CCl4 + HCl Conditions ultra-violet light excess chlorine

Electrophilic addition bromine with ethene Overall reaction equation CH2=CH2 + Br2 CH2BrCH2Br 1,2-dibromoethane mechanism

Electrophilic addition mechanism bromine with ethene H C H C Br + carbocation + - Br Br - CH3 H C Br Br 1,2-dibromoethane reaction equation

Nucleophilic substitution water with bromoethane mechanism CH3CH2Br + H2O CH3CH2OH + HBr ethanol hydroxide ion with bromoethane mechanism CH3CH2Br + OH- (aqueous) CH3CH2OH + Br- ethanol

water with bromoethane Nucleophilic substitution mechanism water with bromoethane CH3 H O C + CH3 H Br C + - Br - O H CH3 H OH C ethanol H Br reaction equation

hydroxide ion with bromoethane Nucleophilic substitution mechanism hydroxide ion with bromoethane CH3 H Br C CH3 H OH C + - Br - - OH ethanol reaction equation

Electrophilic Substitution Nitration of benzene C6H6 + HNO3 C6H5NO2 + H2O Conditions / Reagents concentrated HNO3 and concentrated H2SO4 50oC mechanism

electrophilic substitution mechanism (nitration) 1. Formation of NO2 + the nitronium ion HNO3 + 2H2SO4 NO2 + + 2HSO4- + H3O+ 2. Electrophilic attack on benzene NO2 + + NO2 H O SO3H- NO2 3. Forming the product and re-forming the catalyst H O SO3H reaction equation

Nucleophilic Addition addition of hydrogen cyanide to carbonyls to form hydroxynitriles RCOR + HCN RC(OH)(CN)R RCHO + HCN RCH(OH)CN Conditions / Reagents HCN (aq) and NaOH(aq) to form the CN- nucleophile HCN + OH- CN- + H2O Room temperature and pressure

Nucleophilic Addition Mechanism hydrogen cyanide with propanone CH3COCH3 + HCN CH3C(OH)(CN)CH3 HCN / NaOH (aq) is a source of cyanide ions C N CN + - H CN CH3 C O CN CH3 C O CN H CH3 C O CN 2-hydroxy-2-methylpropanenitrile

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References Steve Lewis for the Royal Society of Chemistry