OCR A Jan 2013 Paper 2 Q7 (with explained solutions) |

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OCR A Jan 2013 Paper 2 Q7

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7 Compound D reacts by nucleophilic substitution and electrophilic addition. 16 CH2 compound D Cl Compound D reacts with KOH(aq) and with HBr(g). The reaction with KOH(aq) is an example of a nucleophilic substitution and the reaction with HBr(g) is an example of electrophilic addition. Describe these two reactions. For each reaction, include:an equation the structure of each organic product the mechanism, using the curly arrow model, showing any relevant dipole the type of bond fission that occurs.OCR 2013<br />
17[12] [Total: 12]OCR 2013 Turn over<br />

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F322/01 Question 7 Answer Mark Scheme January 2013 OH Nucleophilic substitution reaction correct equation for the reaction (cid:57) CH2CHCH2CH2Cl + KOH (cid:198) CH2CHCH2CH2OH + KCl OR C4H7Cl + KOH (cid:198) C4H7OH + KCl correct product of the reaction (cid:57) Mechanism dipole shown on CCl bond: C+ and Clin the correct chloroalkene (cid:57) curly arrow from HO to carbon atom of CCl bond AND curly arrow from CCl bond to chlorine atom (cid:57) formation of Cl(cid:57) Marks Guidance (cid:198) CH2CHCH2CH2OH + Cl ANNOTATE ANSWER WITH TICKS AND CROSSES ETC ALLOW CH2CHCH2CH2Cl + OH ALLOW C4H7Cl + OH (cid:198) C4H7OH + Cl ALLOW correct molecular OR structural OR displayed OR skeletal formula OR mixture of the above For structure of the product ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) if seen ONCE in equation, mechanism or drawn out eg CH2CHCH2CH2OH curly arrow must start from one lone pair on O atom of OH ion OR from negative charge on the O atom of the OH ion Lone pair does not need to be shown on OH ion 23<br />
January 2013 Guidance ANNOTATE ANSWER WITH TICKS AND CROSSES ETC ALLOW SN1 mechanism dipole shown on CCl bond, C+ and Clin correct chloroalkene (cid:57) curly arrow from CCl bond to halogen atom and Cl-(cid:57) curly arrow from OH to correct carbocation (cid:57) curly arrow must start from one lone pair on O atom of OH ion OR from negative charge on the O atom of the OH ion Lone pair does not need to be shown on OH ion F322/01 Question Answer Nucleophilic substitution continued (SN1) Step 1: Mark Scheme Marks Step 2: H2C + CCl H2C + Cl- H2C H2C -OH OH 24<br />
F322/01 Question 7 Answer Mark Scheme January 2013 Cl Br Br CH3CHBrCH2CH2Cl CH2BrCH2CH2CH2Cl Electrophilic addition correct equation for the reaction (cid:57) CH2CHCH2CH2Cl + HBr OR CH2CHCH2CH2Cl + HBr Indication that there are two possible addition products (cid:57) Correct product (cid:57) OR Mechanism Curly arrow from C=C of correct chloroalkene to attack the H atom in HBr (cid:57) Correct dipole on HBr: H+ and Br AND curly arrow from HBr bond to Br (cid:57) Correct carbocation / carbonium ion with the full positive charge shown: C+ AND correct curly arrow from lone pair of Br- to correct carbon atom OR correct curly arrow from negative charge of Br to correct carbon atom (cid:57) Cl Marks Guidance ANNOTATE ANSWER WITH TICKS AND CROSSES ETC ALLOW correct molecular OR structural OR displayed OR skeletal formula OR mixture of the above. eg C4H7Cl + HBr (cid:198) C4H8BrCl For the structure of the product ALLOW correct structural OR displayed OR skeletal formula OR mixture of the above (as long as unambiguous) if seen ONCE in equation, mechanism or drawn out eg CH2BrCH2CH2CH2Cl or CH3CHBrCH2CH2Cl curly arrow must start from covalent bonds and not atoms Lone pair does not need to be shown on ion or used in mechanism DO NOT ALLOW any other partial charges eg shown on double bond DO NOT ALLOW C+ for charge on carbonium ion. Curly arrow from Br can start from the negative charge or the lone pair DO NOT ALLOW delta negative, i.e. Br 25<br />
F322/01 Question 7 Answer Electrophilic addition continued +Br H2C Cl Mark Scheme Marks + Br- Br Cl Cl OR +Br H2C Cl Cl + Br- January 2013 Guidance Br heterolytic fission for both mechanisms and not contradicted (cid:57) Cl 26<br />
F322/01 Question Mark Scheme January 2013 Answer Marks Guidance ALTERNATIVE APPROACH The Candidate who reacts with KOH followed by HBrAward all marks for the nucleophilic substitution mechanism as per the marking schemeYou can award all marks for the electrophilic addition mechanism; however the product will be one of the following: OR OH Br Br OHThe mechanism will be the same except the Cl will now be replaced by OH at every stage Total 12 27<br />

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