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AQA organic reaction mechanisms

AQA organic reaction mechanisms. Click a box below to go to the mechanism. Click here for advice. AS. Free Radical Substitution. Electrophilic Addition. Nucleophilic Substitution. (nitrile hydrolysis reaction). Elimination of HX from haloalkanes. Elimination of water from alcohols.

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AQA organic reaction mechanisms

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  1. AQA organic reaction mechanisms Click a box below to go to the mechanism Click here for advice AS Free Radical Substitution Electrophilic Addition Nucleophilic Substitution (nitrile hydrolysis reaction) Elimination of HX from haloalkanes Elimination of water from alcohols Friedel-Crafts Alkylation Acylation A2 Electrophilic Substitution Nucleophilic Addition Nucleophilic Addition Elimination

  2. 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

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

  4. 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

  5. Electrophilic addition bromine with propene mechanism CH3CH=CH2 + Br2 CH3CHBrCH2Br 1,2-dibromopropane hydrogen bromide with but-2-ene mechanism CH3CH=CHCH3 + HBr CH3CH2CHBrCH3 2-bromobutane concentrated sulphuric acid with but-2-ene mech CH3CH=CHCH3 + HOSO3H CH3CH2CH(OSO3H)CH3 2-butylhydrogensulphate

  6. bromine with propene H H C C H H CH3 H C C H CH3 + Br - Br Br Br + Br Br H H - C C H CH3 Br Br Electrophilic addition mechanism reaction equation carbocation 1,2-dibromopropane

  7. hydrogen bromide with trans but-2-ene CH3 H C C H H CH3 H CH3 C C CH3 + + H H - Br Br H H - CH3 C C CH3 Br H Electrophilic addition mechanism reaction equation carbocation 2-bromobutane

  8. concentrated H2SO4 with cis but-2-ene H H C C H H CH3 CH3 C C CH3 CH3 + + H H - OSO3H OSO3H H H - CH3 C C CH3 H OSO3H Electrophilic addition mechanism reaction equation carbocation 2-butylhydrogensulphate

  9. Nucleophilic substitution hydroxide ion with bromoethane mechanism CH3CH2Br + OH- (aqueous) CH3CH2OH + Br- ethanol cyanide ion with iodoethane mechanism CH3CH2I (ethanol) + CN-(aq) CH3CH2CN + I- propanenitrile ammonia with bromoethane mechanism CH3CH2Br + NH3 2 CH3CH2NH2 + NH4+Br- aminoethane

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

  11. cyanide ion with iodoethane H - + CN C CH3 H H - Br Br C CH3 H - CN Nucleophilic substitution mechanism propanenitrile reaction equation

  12. ammonia with bromoethane - Br - + H NH3 + H H NH3 NH2 Br C C CH3 CH3 H H H - H NH3+Br NH2 C CH3 H Nucleophilic substitution mechanism aminoethane reaction equation

  13. Nitrile hydrolysis Acid hydrolysis of nitriles: CH3CH2CN + H2O + H+ 2 CH3CH2COOH + NH4+ propanoic acid Reflux with strong acid eg HCl (aq)

  14. Elimination of HX from haloalkanes H H - - C C OH Br CH3 H H H H OH C C H CH3 Br H Elimination of HBr from 2-bromopropane + OH- CH3CH=CH2 + H2O + Br- CH3CHBrCH3 (in ethanol) propene acting as a base

  15. Haloalkanes and hydroxide ions alcohol nucleophilic substitution RCH3CH2OH + Br- (aqueous) + OH- hydroxide acts as a nucleophile RCH2CH2X hydroxide acts as a base (ethanol) + OH- elimination RCH=CH2 + H2O + X- alkene

  16. Elimination of water from alcohols Elimination of H2O from propan-1-ol CH3CH2CH2OH CH3CH=CH2 + H2O Heat with concentrated H2SO4

  17. Elimination mechanism – water from propan-1-ol + + H H H H H H H C C OH CH3 C C OH CH3 + H H H H H OH H OH H H H H C C + C C CH3 CH3 H H H protonated alcohol propene carbocation reaction equation

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

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

  20. Friedel-Crafts alkylation Where an H atom attached to an aromatic ring is replaced by a C atom Alkylation of benzene electrophilic substitution C6H6 + RCl C6H5R + HCl R = alkyl group Conditions / Reagents RCl (haloakane) and anhydrous AlCl3 0 - 25oC to prevent further substitution

  21. Alkylation example - Cl AlCl3 + CH3CH2 Cl CH3CH2 With chloroethane overall reaction equation C6H6 + CH3CH2Cl C6H5CH2CH3 + HCl Three steps in electrophilic substitution mechanism 1. Formation of the electrophile (a carbocation) AlCl3

  22. Alkylation electrophilic substitution mechanism 2 - Cl AlCl3 + CH3CH2 H Cl H + CH3CH2 CH3CH2 2. Electrophilic attack on benzene 3. Forming the product and re-forming the catalyst AlCl3 ethylbenzene

  23. Friedel-Crafts acylation An H atom attached to an aromatic ring is replaced by a C atom where C is part of C=O Acylation of benzene electrophilic substitution C6H6 + RCOCl C6H5COR + HCl Conditions / Reagents RCOCl (acyl chloride) and anhydrous AlCl3 50 oC

  24. Acylation example - Cl AlCl3 O + CH3C O CH3C Cl With ethanoyl chloride overall reaction equation C6H6 + CH3COCl C6H5COCH3 + HCl Three steps in electrophilic substitution mechanism 1. Formation of the electrophile (an acylium ion) AlCl3

  25. Acylation electrophilic substitution mechanism 2 - Cl AlCl3 O CH3C H Cl O + CH3C O H CH3C + 2. Electrophilic attack on benzene 3. Forming the product and re-forming the catalyst AlCl3 phenylethanone

  26. Nucleophilic Addition Reduction of carbonyls primary alcohol RCH2OH + 2[H] RCHO secondary alcohol + 2[H] RCOR RCH(OH)R Conditions / Reagents NaBH4 andH2SO4(aq) Room temperature and pressure

  27. Nucleophilic Addition Mechanism + 2[H] RCOR RCH(OH)R H - O + O C CH3 O H C H CH3 CH3 C H CH3 CH3 CH3 H alcohol reduction of propanone NaBH4 is a source of hydride ions fromH2SO4 (aq) H+ H+ propan-2-ol

  28. Nucleophilic Addition addition of hydrogen cyanide to carbonyls to form hydroxynitriles + HCN RCOR RC(OH)(CN)R RCH(OH)CN + HCN RCHO Conditions / Reagents NaCN (aq) andH2SO4(aq) supplies H+ supplies the CN- nucleophile Room temperature and pressure

  29. Nucleophilic Addition Mechanism C N - O + O H O C CH3 C CN CH3 CH3 C CN CH3 CH3 CH3 CN hydrogen cyanide with propanone + HCN CH3COCH3 CH3C(OH)(CN)CH3 NaCN (aq) is a source of cyanide ions fromH2SO4 (aq) H+ H+ 2-hydroxy-2-methylpropanenitrile

  30. Nucleophilic Addition Elimination O R C Acylation of water to give carboxylic acids RCOOH + HCl + H2O RCOCl carboxylic acid OH Conditions room temperature and pressure

  31. Formation of ethanoic acid O CH3 C ethanoyl chloride CH3COCl + H2O CH3COOH + HCl ethanoic acid OH mechanism

  32. Nucleophilic Addition Elimination Mechanism O + C OH CH3 H Cl OH - O O H O + C CH3 + C CH3 C OH CH3 Cl OH H H Cl Cl nucleophilic addition elimination reaction equation

  33. Acylation of primary amines to N-alkyl amides O R C O CH3 C + 2 R’NH2 RCONHR’ + R’NH3+Cl- RCOCl N-alkylamide NHR’ Conditions room temperature and pressure N-propylethanamide NHCH2CH2CH3

  34. Formation of N-propyl ethanamide from 1-aminopropane ethanoyl chloride CH3COCl + CH3CH2CH2NH2 2 CH3CONHCH2CH2CH3 + CH3CH2CH2NH3+Cl- N-propylethanamide mechanism

  35. Nucleophilic Addition Elimination Mechanism O + C NHCH2CH2CH3 CH3 H NHCH2CH2CH3 Cl H - O O O + C CH3 + C CH3 C NHCH2CH2CH3 CH3 Cl NHCH2CH2CH3 H NH2CH2CH2CH3 H Cl Cl + NH2CH2CH2CH3 nucleophilic addition elimination reaction equation

  36. Advice To get back to the mechanism links page from anywhere in the presentation, click the button at the top right corner of the screen. This version provides the organic mechanisms specified (2002/3) by the AQA exam board. Each stage of a reaction equation, its conditions and mechanism are revealed in turn on a mouse click or keyboard stroke. Note that there is another version available where each reaction and mechanism play automatically after an initiating click or key stroke. The number of ways of navigating through this presentation may depend on the version of PowerPoint being used and how it is configured. Some possible ways of advancing: left mouse click or return key or right arrow key or up arrow key. Some possible ways of reversing: backspace key or left arrow key or down arrow key.

  37. References Steve Lewis for the Royal Society of Chemistry

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