Edexcel organic reaction mechanisms Click a box below

Edexcel organic reaction mechanisms Click a box below to go to the mechanism Homolytic Click here for advice Free Radical Substitution Free Radical Addition Heterolytic Electrophilic Addition Nucleophilic Substitution Electrophilic Substitution SN 2 Nitration SN 1 Br 2 Alkylation Acylation Nucleophilic Addition Original slide prepared for the

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

Free radical substitution mechanism Cl H 3 C Cl ultra-violet Cl Cl initiation step Cl H 3 C H Cl Cl H 3 C Cl CH 3 H 3 C CH 3 two propagation steps termination step minor termination step Original slide prepared for the

Further free radical substitutions Overall reaction equations CH 3 Cl + Cl 2 CH 2 Cl 2 + HCl CH 2 Cl 2 + Cl 2 CHCl 3 + HCl CHCl 3 + Cl 2 CCl 4 + HCl Conditions ultra-violet light excess chlorine Original slide prepared for the

Free radical addition polymerisation of ethene i. e. homolytic breaking of covalent bonds Overall reaction equation n H 2 C=CH 2 ethene [ CH 2 ]n polyethene Conditions free radical source (a species that generates free radicals that allow the polymerisation of ethene molecules) Original slide prepared for the

Free radical addition mechanism R H 2 C CH 2 R R H 2 C initiation step CH 2 R H 2 C CH 2 R CH 2 CH 2 R chain propagation steps Addition of H 2 C=CH 2 repeats the same way until: R(CH 2)n. CH 2 H 2 C(CH 2)m. R termination step R(CH 2)n. CH 2(CH 2)m. R polyethene Original slide prepared for the

Electrophilic addition bromine with propene CH 3 CH=CH 2 + Br 2 mechanism CH 3 CHBr. CH 2 Br 1, 2 -dibromopropane hydrogen bromide with but-2 -ene CH 3 CH=CHCH 3+ HBr mechanism CH 3 CH 2 CHBr. CH 3 2 -bromobutane Original slide prepared for the

Electrophilic addition mechanism bromine with propene H reaction equation H C C CH 3 H H Br - carbocation CH 3 C + + Br H C H Br H H Br CH 3 C C Br Br 1, 2 -dibromopropane Br H Br Original slide prepared for the

Electrophilic addition mechanism hydrogen bromide with trans but-2 -ene reaction equation CH 3 H C C CH 3 H H + Br - H H carbocation CH 3 C + C CH 3 Br H H H CH 3 C C Br H CH 3 2 -bromobutane Original slide prepared for the

Nucleophilic substitution hydroxide ion with bromoethane CH 3 CH 2 Br + OH- (aqueous) mechanism CH 3 CH 2 OH + Brethanol hydroxide ion with 2 -bromo, 2 -methylpropane mechanism (CH 3)3 CBr+ OH- (aqueous) (CH 3)3 COH + Br 2 -methylpropan-2 -ol Original slide prepared for the

Nucleophilic substitution mechanism hydroxide ion with bromoethane H + CH 3 C H Br CH 3 C H OH- (SN 2) OH H SN 2 Br ethanol reaction equation S (substitution) N(nucleophilic) 2(species reacting in the slowest step) Original slide prepared for the

Nucleophilic substitution mechanism OH- ion with 2 -bromo, 2 -methylpropane (SN 1) - CH 3 + CH 3 C Br CH 3 C+ CH 3 SN 1 CH 3 Br OH CH 3 OH- 2 -methylpropan-2 -ol reaction equation S (substitution) N(nucleophilic) 1(species reacting in the slowest step) Original slide prepared for the

Nucleophilic substitution cyanide ion with iodoethane CH 3 CH 2 I (ethanol) + CN-(aq) mechanism CH 3 CH 2 CN + Ipropanenitrile cyanide ion with 2 -bromo, 2 -methylpropane mechanism (CH 3)3 CBr (ethanol) + CN- (aqueous) (CH 3)3 CCN + Br 2, 2 -dimethylpropanenitrile Original slide prepared for the

Nucleophilic substitution mechanism cyanide ion with iodoethane (SN 2) H + CH 3 C I H - CH 3 C H CN- CN H I - propanenitrile SN 2 S (substitution) N(nucleophilic) 2(species reacting in the slowest step) reaction equation Original slide prepared for the

Nucleophilic substitution mechanism CN- ion with 2 -bromo, 2 -methylpropane (SN 1) - CH 3 + CH 3 C Br CH 3 C+ CH 3 C CH 3 SN 1 CH 3 Br CN CH 3 CN- 2, 2 -dimethyl propanenitrile S (substitution) N(nucleophilic) 1(species reacting in the slowest step) reaction equation Original slide prepared for the

Electrophilic Substitution Nitration of benzene Where an H atom attached to an aromatic ring is replaced by an NO 2 group of atoms C 6 H 6 + HNO 3 C 6 H 5 NO 2 + H 2 O Conditions / Reagents concentrated HNO 3 and concentrated H 2 SO 4 50 o. C mechanism Original slide prepared for the

electrophilic substitution mechanism (nitration) + 1. Formation of NO 2 the nitronium ion + HNO 3 + 2 H 2 SO 4 NO 2 + 2 HSO 4 - + H 3 O+ 2. Electrophilic attack on benzene + NO 2 H O SO 3 H 3. Forming the product and re-forming the catalyst reaction equation - NO 2 H O SO 3 H Original slide prepared for the

Bromination of benzene Where an H atom attached to an aromatic ring is replaced by a Br atom electrophilic substitution C 6 H 6 + Br 2 C 6 H 5 Br + HBr R = alkyl group Conditions / Reagents Br 2 and anhydrous Al. Br 3 25 o. C Original slide prepared for the

Electrophilic substitution mechanism 1. Formation of the electrophile Br Br Al. Br 3 + Br 2. Electrophilic attack on benzene + Br Br H + 3. Forming the products Br - Al. Br 3 - Br Al. Br 3 Br and re-forming the catalyst bromobenzene H Br Al. Br 3 Original slide prepared for the

Alkylation of benzene Where an H atom attached to an aromatic ring is replaced by a C atom electrophilic substitution C 6 H 6 + RCl C 6 H 5 R + HCl R = alkyl group Conditions / Reagents RCl (haloakane) and anhydrous Al. Cl 3 0 - 25 o. C to prevent further substitution Original slide prepared for the

Alkylation example With chloroethane C 6 H 6 + CH 3 CH 2 Cl overall reaction equation C 6 H 5 CH 2 CH 3 + HCl Three steps in electrophilic substitution mechanism 1. Formation of the electrophile (a carbocation) CH 3 CH 2 Cl Al. Cl 3 + CH 3 CH 2 Cl - Al. Cl 3 Original slide prepared for the

Alkylation electrophilic substitution mechanism 2 2. Electrophilic attack on benzene + CH 3 CH 2 H + - Cl Al. Cl 3 3. Forming the product and re-forming the catalyst CH 3 CH 2 H Al. Cl 3 Cl ethylbenzene Original slide prepared for the

Acylation of benzene An H atom attached to an aromatic ring is replaced by a C atom where C is part of C=O electrophilic substitution C 6 H 6 + RCOCl C 6 H 5 COR + HCl Conditions / Reagents RCOCl (acyl chloride) and anhydrous Al. Cl 3 50 o. C Original slide prepared for the

Acylation example With ethanoyl chloride overall reaction equation C 6 H 6 + CH 3 COCl C 6 H 5 COCH 3 + HCl Three steps in electrophilic substitution mechanism 1. Formation of the electrophile (an acylium ion) O CH 3 C Cl + CH 3 C O Al. Cl 3 Cl - Al. Cl 3 Original slide prepared for the

Acylation electrophilic substitution mechanism 2 2. Electrophilic attack on benzene O + CH 3 C O CH 3 C + H Cl 3. Forming the products and re-forming the catalyst O CH 3 C - Al. Cl 3 H Cl Al. Cl 3 phenylethanone Original slide prepared for the

Nucleophilic Addition addition of hydrogen cyanide to carbonyls to form hydroxynitriles RCOR + HCN RCHO + HCN RC(OH)(CN)R RCH(OH)CN Conditions / Reagents Na. CN (aq) and H 2 SO 4(aq) supplies H+ supplies the CN- nucleophile Room temperature and pressure Original slide prepared for the

Nucleophilic Addition Mechanism hydrogen cyanide with propanone CH 3 COCH 3 + HCN CH 3 C(OH)(CN)CH 3 Na. CN (aq) is a source of cyanide ions + CH 3 C O - CH 3 CN H+ from H 2 SO 4 (aq) H+ O CH 3 CN C N O CH 3 C H CN CH 3 2 -hydroxy-2 -methylpropanenitrile Original slide prepared for the

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 Edexcel 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 Power. Point 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. Original slide prepared for the

References Steve Lewis for the Royal Society of Chemistry Original slide prepared for the