OCR A Jun 2017 Paper 2 Q6 (with explained solutions) |

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OCR A Jun 2017 Paper 2 Q6

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14 6 Organic compounds can be prepared in the laboratory using synthetic routes with two or more stages. (a) A student devises a two-stage synthesis of cyclohexene from bromocyclohexane. Br Step 1 NaOH(aq) Intermediate E Step 2 bromocyclohexane cyclohexene (i) Suggest the structure of intermediate E and the reagent(s) and conditions for step 2. reagent(s) and conditions[2] (ii) The student carries out this synthesis and obtains 1.23 g of pure cyclohexene from 5.50 g of bromocyclohexane. Calculate the percentage yield of cyclohexene. Give your final answer to an appropriate number of significant figures. percentage yield =% [3]<br />
15 (b) Cyclohexene is reacted with bromine to prepare the organic compound F. Give the structure of compound F and outline the mechanism for this reaction. Include curly arrows, charges and relevant dipoles. [4] END OF QUESTION PAPER<br />

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H032/02 Question (i) (a) Answer Mark scheme Marks Acid (catalyst) AND heat(ii) FIRST CHECK THE ANSWER ON THE ANSWER LINE IF answer = 44.4(%) award all 3 marks for calculation Amount cyclohexene (m/M) = 1.23/82 OR 0.0150 molAmount of bromocyclohexane (m/M) = 5.50/162.9 OR 0.0338 mol% yield = (0.0150/0.0338)100 = 44.4(%)Final answer must be to 3 significant figures (b) 20 June 2017 Guidance ALLOW correct structural OR displayed OR skeletal formulae OR a combination of above as long as unambiguous ALLOW (heat under) reflux ALLOW H3PO4 OR H2SO4 OR H+ DO NOT ALLOW other named acids IGNORE concentration/pressure IGNORE water/steam If there is an alternative answer, check to see if there is any ECF credit possible ALLOW 3 SF: 0.0338 up to calculator value of 0.033763044 correctly rounded Common ECFs (2 marks) Incorrect Mrincorrect moles of cyclohexene Incorrect Mrincorrect moles of 2- bromocyclohexane e.g. ALLOW two marks for use of incorrect mass of bromocyclohexane with other calculations correct e.g. (5.50/163) = 0.03374233144.5% ALLOW calculation in mass Theoretical mass yield: m(C6H10) = 0.033882 = 2.77 g % yield = (1.23/2.77)100 = 44.4% ANNOTATE ANSWER WITH TICKS AND<br />
H032/02 Question Mark scheme June 2017 Answer Marks Guidance Curly arrow from double bond to Br of BrBrCorrect dipole shown on BrBr AND curly arrow showing breaking of BrBr bondOR Correct carbocation with + charge on C with 3 bonds AND curly arrow from Br to C+ of carbocationCorrect product: OR CROSSES ETC Curly arrow must start from bond and go to correct atom DO NOT ALLOW any other partial charges e.g. shown on double bond DO NOT ALLOW missing H on displayed formulae (penalise once only) DO NOT ALLOW + on C of carbocation. Curly arrow must come from a lone pair on Br OR from the negative sign of Br on Br IGNORE wording if diagrams are correct Maximum of two marks for mechanism based on incorrect structure of cyclohexene ion does not need to be shown) ion (then lone pair Total 21<br />

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