OCR A Jan 2011 Paper 4 Q3 (with explained solutions) |

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OCR A Jan 2011 Paper 4 Q3

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3 Safranal, shown below, is an aldehyde which contributes to the aroma of saffron. H3C CH3 CH3 safranal An undergraduate chemist investigated some reactions of safranal. (a) She prepared a solution of Tollens reagent and added a few drops of safranal. She then warmed the mixture for about 5 minutes in a water bath. Describe what you would expect the chemist to see. State the type of reaction that the safranal undergoes. Draw the structure of the organic product formed in this reaction.[3]OCR 2011<br />
(b) The chemist then reduced safranal using an aqueous solution of NaBH4. Outline the mechanism for this reaction. Use curly arrows and show any relevant dipoles. can be used to represent safranal. [4] (c) Suggest one reaction of safranal that does not involve the aldehyde group. State the reagent, observation (if any) and draw the organic product. reagentobservationorganic product [3] [Total: 10]OCR 2011 Turn over<br />

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F324 Question Answer 3 (a) observation: silver OR Ag (cid:57) type of reaction: oxidation(cid:57) organic product: H3C CH3 OH (b) CH3 (cid:57) (cid:71) C (cid:71) O OH (+ OH intermediate products 1 mark for curly arrow from H to C of C=O (cid:57) 1 mark for correct dipole on C=O AND curly arrow from double bond to O(cid:71) (cid:57) 1 mark for correct intermediate with negative charge on O AND curly arrow from O to H of HOH AND curly arrow from HO to O of HOH (cid:57) 1 mark for correct organic product (cid:57) Mark Scheme January 2011 Mark Guidance ALLOW black OR grey ALLOW redox ALLOW correct structural OR displayed OR skeletal formula ALLOW combination of formulae as long as unambiguous DO NOT ALLOW molecular formulae ALLOW carboxylate, COO ANNOTATIONS MUST BE USED ALLOW mechanism showing curly arrows from lone pair on H and O of intermediate Dipole not required on HOH DO NOT ALLOW incorrect dipole on HOH ALLOW 1 mark for correct intermediate withcharge on O AND curly arrow from O to H+ IGNORE missing OH DO NOT ALLOW incorrect second product<br />
F324 Mark Scheme January 2011 Question Answer 3 (c) reagent: Br2 (cid:57) observation: decolourised OR orange to colourless (cid:57) organic product: (cid:57) CH3 H3C Br Br CH3 Br Br Total 10 Mark Guidance DO NOT ALLOW ECF from incorrect reagent, eg 2,4-DNP DO NOT ALLOW goes clear ALLOW red/orange/yellow/brown in any combination ALLOW organic product from reaction of one of the double bonds only, ie H3C CH3 Br H3C CH3 CH3 OR Br Br CH3 Br ALLOW correct structural OR displayed OR skeletal formula ALLOW combination of formulae as long as unambiguous DO NOT ALLOW molecular formulae ALTERNATIVE reagents For 1st mark, ALLOW H2 OR Cl2 OR I2 OR HCl OR HBr OR HI OR H2O For 2nd mark, there must be a statement of no change OR no observation or similar that implies there is no visible change EXCEPT for I2 which has an observation of decolourised OR brown to colourless For 3rd mark, correct organic product must be shown that could be from reaction of both or one of the double bonds.<br />

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