OCR A Jun 2017 Paper 2 Q18 (with explained solutions) |

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OCR A Jun 2017 Paper 2 Q18

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18 This question is about organic compounds containing nitrogen. 18 (a) Sodium cyanide, NaCN, can be reacted with many organic compounds to increase the length of a carbon chain. (i) 1-Chloropropane, CH3CH2CH2Cl, reacts with ethanolic sodium cyanide by nucleophilic substitution. Outline the mechanism for this reaction. Include curly arrows, relevant dipoles and the structure of the organic product. [3]<br />
19 BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE<br />
(ii) Compound G is used to synthesise compounds H and I as shown in the flowchart below. Complete the flowchart showing the structure of compound G and the formulae of the reagents for Reaction 2 and Reaction 3. 20 OH OH compound I Reaction 3 reagents:Reaction 1 NaCN/H+ OH CN compound G Reaction 2 reagents:OH compound H NH2 [3]<br />
(iii) Compound H reacts with dilute hydrochloric acid to form a salt. 21 Explain why compound H can react with dilute hydrochloric acid and suggest a structure for the salt formed. ExplanationStructure (iv) Compound I is the monomer for the biodegradable polymer J. Draw two repeat units of polymer J and suggest a reason why it is biodegradable. [2][3]<br />
22 (b) The repeat unit of Nylon 6,6 is shown below. N H Nylon 6,6 H N (i) Draw the structures of two monomers that can be used to form Nylon 6,6. (ii) A sample of Nylon 6,6 has a relative molecular mass of 21500. Estimate the number of repeat units in the sample. Give your answer as a whole number. [2] number of repeat units =[1]<br />

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H432/02 Question 18 (a) (i) Mark Scheme June 2017 Answer to carbon atom of CCl bondcurly arrow from CN Dipole shown on CCl bond, C+ AND curly arrow from CCl bond to Cl atomand Cl, --------------------------------------------------------------------- correct organic product AND ClMarks Guidance ANNOTATE ANSWER WITH TICKS AND CROSSES Curly arrow must come from lone pair on C of CN OR CN OR from minus sign on C of CN ion (then lone pair on CN does not need to be shown) IGNORE NaCl --------------------------------------------------------------------- ALLOW SN1 mechanism: Dipole shown on CCl bond, C+ AND curly arrow from CCl bond to Cl atomCorrect carbocation AND curly arrow from CN to carbocation. Curly arrow must come from lone pair on C of CN OR CN OR from minus sign on C of CN ion (then lone pair on CN does not need to be shown)correct organic product AND Cland Cl, 18<br />
H432/02 Question (ii) Compound G Answer Mark Scheme MarksReagents Reaction 2: H2 AND NiReaction 3: Correct formula of an aqueous acid e.g. HCl(aq)/H2SO4(aq)19 June 2017 Guidance ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous IGNORE name(s) ALLOW ALLOW any suitable metal catalyst e.g. Pt ALLOW LiAlH4 for reagent in reaction 2 DO NOT ALLOW NaBH4 for reagent in reaction 2 IGNORE names (question asks for formulae) IGNORE references to temperature and/or pressure ALLOW H+(aq) IGNORE dilute ALLOW formula of an acid AND water e.g. HCl AND H2O H2SO4 AND H2O<br />
H432/02 Question (iii) Explanation Answer Mark Scheme Marks Nitrogen electron pair OR nitrogen lone pair AND accepts a proton/H+Structure of salt AND ClJune 2017 Guidance IGNORE NH2 group donates electron pair ALLOW nitrogen donates an electron pair to H+ DO NOT ALLOW nitrogen donates lone pair to acid IGNORE comments about the O in the OH group Compound H is a base is not sufficient (role of lone pair required) DO NOT ALLOW nitrogen/N lone pair accepts hydrogen (proton/H+ required) ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous ALLOW i.e. charges not required IF charges are shown both need to be present ALLOW charge either on N atom or NH3 IF displayed then + charge must be on the nitrogen 20<br />
H432/02 Question (iv) Answer Mark Scheme Marks Ester linkRest of structure(polymer J is biodegradable because) the ester / ester bond / ester group / polyester can be hydrolysed(b) (i) (n = = ) 95 (repeat units)21500 226 (ii) June 2017 Guidance ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous DO NOT ALLOW more than two repeat units for second marking point. End bonds MUST be shown (do not have to be dotted) IGNORE brackets IGNORE n Broken down by water is not sufficient IGNORE references to photodegradable ALLOW any combination of skeletal OR structural OR displayed formula as long as unambiguous ALLOW MUST be a whole number. DO NOT ALLOW an answer that uses an incorrect molar mass in the working. ALLOW 96 Total 14 21<br />

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